bluuebunny/crossref_metadata_2025 huggingface dataset:
A short proof of Weyl's law for fractional differential operators
Authors: Geisinger Leander
Published: January 2014

We study spectral asymptotics for a large class of differential operators on an open subset of \documentclass[12pt]{minimal}\begin{document}$\mathbb {R}^d$\end{document}Rd with finite volume. This class includes the Dirichlet Laplacian, the fractional Laplacian, and also fractional differential operators with non-homogeneous symbols. Based on a sharp estimate for the sum of the eigenvalues we establish the first term of the semiclassical asymptotics. This generalizes Weyl's law for the Laplace operator.
Annealing temperature and thickness dependence of magnetic properties in epitaxial L1-Mn1.4Ga films
Authors: Zheng Y. H. , Han G. C. , Lu H. , Teo K. L.
Published: January 2014

Mn1.4Ga films with high perpendicular magnetic anisotropy and high crystalline quality were grown on MgO substrates with Cr buffer layer using molecular beam epitaxy. The crystalline structure and the surface morphology of the films have been systematically investigated as functions of in-situ annealing temperature (Ta) and film thickness. It is found that the magnetic properties can be largely tuned by adjusting Ta. As Ta increases, both saturation magnetization (Ms) and uniaxial perpendicular magnetic anisotropy constant (Ku) increase to the maximum values of 612 emu/cc and 18 Merg/cc at 300 °C, respectively, and then decrease. The morphology also changes with Ta, showing a minimum roughness of 2.2 Å at Ta = 450 °C. On the other hand, as the thickness increases, Ms and Ku increase while coercivity decreases, which indicates there is a magnetic dead layer with a thickness of about 1.5 nm at the interfaces. The detailed examination on the surface morphology of the films with various thicknesses shows a complicated film growth process, which can be understood from the relaxation mechanism of the interfacial strain.
Temperature dependence of magnetic properties of heat treated cobalt ferrite
Authors: Nlebedim I. C. , Melikhov Y. , Jiles D. C.
Published: January 2014

This study demonstrates the effectiveness of heat treatment in optimizing the magnetic properties of cobalt ferrite, compared to other methods such as cation substitution. It also shows how the magnetic properties of the heat treated cobalt ferrite vary under different temperature conditions. Saturation magnetization increased more due to heat treatment than due to Zn-substitution; a cation substitution that is known to result in high saturation magnetization in ferrites. A remarkable observation is that the increase in the saturation magnetization due to heat treatment was not at the expense of Curie temperature as was often reported for cation substituted materials. The observed variations in the magnetic properties were explained on the basis of cation redistribution arising as a result of the heat treatment.
Compact representation of wall-bounded turbulence using compressive sampling
Authors: Bourguignon J.-L. , Tropp J. A. , Sharma A. S. , McKeon B. J.
Published: January 2014

Compressive sampling is well-known to be a useful tool used to resolve the energetic content of signals that admit a sparse representation. The broadband temporal spectrum acquired from point measurements in wall-bounded turbulence has precluded the prior use of compressive sampling in this kind of flow, however it is shown here that the frequency content of flow fields that have been Fourier transformed in the homogeneous spatial (wall-parallel) directions is approximately sparse, giving rise to a compact representation of the velocity field. As such, compressive sampling is an ideal tool for reducing the amount of information required to approximate the velocity field. Further, success of the compressive sampling approach provides strong evidence that this representation is both physically meaningful and indicative of special properties of wall turbulence. Another advantage of compressive sampling over periodic sampling becomes evident at high Reynolds numbers, since the number of samples required to resolve a given bandwidth with compressive sampling scales as the logarithm of the dynamically significant bandwidth instead of linearly for periodic sampling. The combination of the Fourier decomposition in the wall-parallel directions, the approximate sparsity in frequency, and empirical bounds on the convection velocity leads to a compact representation of an otherwise broadband distribution of energy in the space defined by streamwise and spanwise wavenumber, frequency, and wall-normal location. The data storage requirements for reconstruction of the full field using compressive sampling are shown to be significantly less than for periodic sampling, in which the Nyquist criterion limits the maximum frequency that can be resolved. Conversely, compressive sampling maximizes the frequency range that can be recovered if the number of samples is limited, resolving frequencies up to several times higher than the mean sampling rate. It is proposed that the approximate sparsity in frequency and the corresponding structure in the spatial domain can be exploited to design simulation schemes for canonical wall turbulence with significantly reduced computational expense compared with current techniques.
Physical properties and analytical models of band-to-band tunneling in low-bandgap semiconductors
Authors: Shih Chun-Hsing , Dang Chien Nguyen
Published: January 2014

Low-bandgap semiconductors, such as InAs and InSb, are widely considered to be ideal for use in tunnel field-effect transistors to ensure sufficient on-current boosting at low voltages. This work elucidates the physical and mathematical considerations of applying conventional band-to-band tunneling models in low-bandgap semiconductors, and presents a new analytical alternative for practical use. The high-bandgap tunneling generates most at maximum field region with shortest tunnel path, whereas the low-bandgap generations occur dispersedly because of narrow tunnel barrier. The local electrical field associated with tunneling-electron numbers dominates in low-bandgap materials. This work proposes decoupled electric-field terms in the pre-exponential factor and exponential function of generation-rate expressions. Without fitting, the analytical results and approximated forms exhibit great agreements with the sophisticated forms both in high- and low-bandgap semiconductors. Neither nonlocal nor local field is appropriate to be used in numerical simulations for predicting the tunneling generations in a variety of low- and high-bandgap semiconductors.
Effect of band alignment on photoluminescence and carrier escape from InP surface quantum dots grown by metalorganic chemical vapor deposition on Si
Authors: Halder Nripendra N. , Biswas Pranab , Dhabal Das Tushar , Das Sanat Kr. , Chattopadhyay S. , Biswas D. , Banerji P.
Published: January 2014

A detailed analysis of photoluminescence (PL) from InP quantum dots (QDs) grown on Si has been carried out to understand the effect of substrate/host material in the luminescence and carrier escape process from the surface quantum dots. Such studies are required for the development of monolithically integrated next generation III-V QD based optoelectronics with fully developed Si microelectronics. The samples were grown by atmospheric pressure metalorganic chemical vapor deposition technique, and the PL measurements were made in the temperature range 10–80 K. The distribution of the dot diameter as well as the dot height has been investigated from atomic force microscopy. The origin of the photoluminescence has been explained theoretically. The band alignment of InP/Si heterostructure has been determined, and it is found be type II in nature. The positions of the conduction band minimum of Si and the 1st excited state in the conduction band of InP QDs have been estimated to understand the carrier escape phenomenon. A blue shift with a temperature co-efficient of 0.19 meV/K of the PL emission peak has been found as a result of competitive effect of different physical processes like quantum confinement, strain, and surface states. The corresponding effect of blue shift by quantum confinement and strain as well as the red shift by the surface states in the PL peaks has been studied. The origin of the luminescence in this heterojunction is found to be due to the recombination of free excitons, bound excitons, and a transition from the 1st electron excited state in the conduction band (e1) to the heavy hole band (hh1). Monotonic decrease in the PL intensity due to increase of thermally escaped carriers with temperature has been observed. The change in barrier height by the photogenerated electric-field enhanced the capture of the carriers by the surface states rather than their accumulation in the QD excited state. From an analysis of the dependence of the PL intensity, peak position, and line width with temperature and excitation source, the existence of free and bound excitonic recombination together with e1 → hh1 transitions in the QDs is established.
Large-scale analysis of self-similar unstably stratified homogeneous turbulence
Authors: Soulard Olivier , Griffond Jérôme , Gréa Benoît-Joseph
Published: January 2014

The large-scale properties of self-similar unstably stratified homogeneous (USH) turbulence are investigated using an eddy-damped quasi-normal markovianized approximation of the nonlinear term. This analysis shows that a special role is played by the wave vectors contained in the equatorial plane, i.e., the plane perpendicular to gravity. It is indeed in this plane that turbulent spectra reach their maxima and evolve linearly from their initial condition when their initial infrared exponent is smaller than 4. At other angles, this property is not satisfied and turbulent spectra eventually undergo an evolution dominated by nonlinear backscattering processes. The self-similar evolution of USH turbulence is also shown to be related to the properties of large scales. In particular, the asymptotic growth rate of the mixing length depends on the initial infrared exponent in the equatorial plane. Besides, the self-similar asymptotic values of the concentration and velocity correlations also depend on the properties of large scales. This allows to derive relations between the correlations and the growth rate parameter.
Rheological effects in the 3D creeping flow past a sedimenting sphere subject to orthogonal shear
Authors: Housiadas Kostas D. , Tanner Roger I.
Published: January 2014

The effects of the rheological parameters of nonlinear differential constitutive models in the isothermal, steady, creeping, flow past a sedimenting sphere, in an incompressible viscoelastic matrix fluid, subject to simple shear in a plane perpendicular to the direction of sedimentation are studied analytically. The viscoelasticity of the ambient fluid is modeled using the Upper Convected Maxwell, Oldroyd-B, exponential Phan-Thien-Tanner, Giesekus, and FENE-P constitutive equations. The solution of the governing equations is expanded as a regular perturbation series for small values of the Deborah number, and the resulting sequence of three-dimensional partial differential equations is solved analytically up to fourth order. Approximate analytical expressions for the angular velocity of the rigid sphere, as well as for the drag force on the sphere, are derived and discussed. The solutions reveal both the increase of the drag in case of Boger-type fluids (modeled with the FENE-P model) and the decrease of the drag in case of elastic fluids (modeled with the Giesekus model).
Group theoretical construction of planar noncommutative phase spaces
Authors: Ngendakumana Ancille , Nzotungicimpaye Joachim , Todjihoundé Leonard
Published: January 2014

Noncommutative phase spaces are generated and classified in the framework of centrally extended anisotropic planar kinematical Lie groups as well as in the framework of noncentrally abelian extended planar absolute time Lie groups. Through these constructions the coordinates of the phase spaces do not commute due to the presence of naturally introduced fields giving rise to minimal couplings. By symplectic realizations methods, physical interpretations of generators coming from the obtained structures are given.
Power-law versus log-law in wall-bounded turbulence: A large-eddy simulation perspective
Authors: Cheng W. , Samtaney R.
Published: January 2014

The debate whether the mean streamwise velocity in wall-bounded turbulent flows obeys a log-law or a power-law scaling originated over two decades ago, and continues to ferment in recent years. As experiments and direct numerical simulation can not provide sufficient clues, in this study we present an insight into this debate from a large-eddy simulation (LES) viewpoint. The LES organically combines state-of-the-art models (the stretched-vortex model and inflow rescaling method) with a virtual-wall model derived under different scaling law assumptions (the log-law or the power-law by George and Castillo [“Zero-pressure-gradient turbulent boundary layer,” Appl. Mech. Rev. 50, 689 (1997)]). Comparison of LES results for Reθ ranging from 105 to 1011 for zero-pressure-gradient turbulent boundary layer flows are carried out for the mean streamwise velocity, its gradient and its scaled gradient. Our results provide strong evidence that for both sets of modeling assumption (log law or power law), the turbulence gravitates naturally towards the log-law scaling at extremely large Reynolds numbers.
Photoluminescence imaging for determining the spatially resolved implied open circuit voltage of silicon solar cells
Authors: Hallam Brett , Tjahjono Budi , Trupke Thorsten , Wenham Stuart
Published: January 2014

Photoluminescence imaging has widely been used as a characterisation tool for the development of silicon solar cells. However, photoluminescence images typically only give qualitative information due to the presence of an unknown calibration constant. In this work, quasi-steady-state photoconductance measurements on partially processed solar cells and I-V measurements on finished solar cells are used to determine the calibration constants to yield spatially resolved implied open circuit voltage images. This technique is then applied to determine the implied open circuit voltage of laser doped selective emitter solar cells at various stages of cell fabrication after the formation of the full area aluminium back surface field when other characterisation techniques such as photoconductance cannot be used.
Time-integrated photoluminescence and pump-probe reflection spectroscopy of Si doped InN thin films
Authors: Mohanta Antaryami , Jang Der-Jun , Wang Ming-Sung , Tu L. W.
Published: January 2014

Temperature and excitation power dependent time-integrated photoluminescence of Si doped InN thin films are investigated. Photoluminescence (PL) spectra at low temperatures are described by single emission peak ensued due to “free-to-bound” recombination; whereas PL spectra at higher temperatures above 150 K are characterized by both “band-to-band” and “free-to-bound” transition. Carrier dynamics of Si doped InN thin films is studied using pump-probe reflection spectroscopy at room temperature. The hot electron cooling process is well described by electron-electron scattering. The dependence of the hot electron cooling rate on total electron density shows sublinear to linear behavior with increase of background electron density. The variation of the carrier recombination lifetime with total electron density implicates the dominance of the defect-related nonradiative recombination channel over other recombination processes.
Optical properties of WO3 thin films using surface plasmon resonance technique
Authors: Paliwal Ayushi , Sharma Anjali , Tomar Monika , Gupta Vinay
Published: January 2014

Indigenously assembled surface plasmon resonance (SPR) technique has been exploited to study the thickness dependent dielectric properties of WO3 thin films. WO3 thin films (80 nm to 200 nm) have been deposited onto gold (Au) coated glass prism by sputtering technique. The structural, optical properties and surface morphology of the deposited WO3 thin films were studied using X-ray diffraction, UV-visible spectrophotometer, Raman spectroscopy, and Scanning electron microscopy (SEM). XRD analysis shows that all the deposited WO3 thin films are exhibiting preferred (020) orientation and Raman data indicates that the films possess single phase monoclinic structure. SEM images reveal the variation in grain size with increase in thickness. The SPR reflectance curves of the WO3/Au/prism structure were utilized to estimate the dielectric properties of WO3 thin films at optical frequency (λ = 633 nm). As the thickness of WO3 thin film increases from 80 nm to 200 nm, the dielectric constant is seen to be decreasing from 5.76 to 3.42, while the dielectric loss reduces from 0.098 to 0.01. The estimated value of refractive index of WO3 film is in agreement to that obtained from UV-visible spectroscopy studies. The strong dispersion in refractive index is observed with wavelength of incident laser light.
Switching current density reduction in perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions
Authors: You Chun-Yeol
Published: January 2014

We investigate the switching current density reduction of perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions using micromagnetic simulations. We find that the switching current density can be reduced with elongated lateral shapes of the magnetic tunnel junctions, and additional reduction can be achieved by using a noncollinear polarizer layer. The reduction is closely related to the details of spin configurations during switching processes with the additional in-plane anisotropy.
Fuzzy based prediction of wind distributed generation impact on distribution network: Case study—Banat region, Serbia
Authors: Žarković Mileta , Šošić Darko , Dobrić Goran
Published: January 2014

The paper proposes the methodology for the assessment of impact that wind distributed generation can have on distribution network. Effects of active power losses, voltage drops, and voltage total harmonic distortion are considered. The methodology uses fuzzy logic in order to address uncertainties in wind energy generation, as well as artificial neural networks for wind speed assessment. Measurement data of temperature, irradiation, and wind direction at different wind turbine hub heights are used. The predicted wind speed, active power loss variation, and elasticity of power quality constraints are presented in a form of fuzzy numbers. The proposed methodology is tested on realistic, 28-bus 35 kV voltage distribution system in the Banat region in Serbia. A steady-state voltage stability index is applied to select wind distribution generation locations. It is shown that wind distributed generation can improve voltage regulation and reduce active power losses. However, increase in voltage total harmonic distortion is possible. The proposed methodology enables analysis of the impact that wind speed has on possible effects of wind distributed generation.
Strain tuning of native defect populations: The case of Cu2ZnSn(S,Se)4
Authors: Zhu Junyi , Liu Feng , Scarpulla Michael A.
Published: January 2014

Native defects are ubiquitous especially in compound semiconductors and dominate the properties of many materials. Applying first principles calculations, we propose a novel strategy to tune native defect populations in Cu2ZnSn(S,Se)4 which is an emerging photovoltaic absorber material. The formation of Cu vacancies (VCu), which are predicted to be shallower acceptors than Cu on Zn antisites (CuZn), can be greatly promoted by compressive strain. Additionally, nonlinearities are found in the strain dependence of the VCu formation energy. Both uniform and non-uniform strains may be present in physical samples implying probable variations in native defect concentrations.
Strategy for optimal location and rating of wind power generator with maximization of social welfare in double auction competitive power market
Authors: Sharma Naveen Kumar , Raj Sood Yog
Published: January 2014

This paper presents a generalized optimal model for determining the location and rating of wind power generation in double auction competitive power market. The optimization technique has been used with an objective to maximizing the social welfare and profit to wind gencos company (WP-GENCO) while consider all system constraints. The performance of any electricity market is assessed by its impact on social welfare, which may be defined as “the difference of the benefit of the energy to society as measured by society's willingness to pay for its demand and the cost of energy.” Each distribution company (Disco) will pay an amount to independent system operator (ISO) for purchase the power and each generation company (Genco) will receive an amount from the ISO to sale the power. The amount to be paid by each Disco and amount to be received by each Genco has been determined by pay as bidding price approach. The social welfare has been then determined based on total payments and receipts. The proposed approach has been applied to modified IEEE 30-bus test system in which bidding at all generator buses and some load buses has been introduced.
Plasmonic tunable metamaterial absorber as ultraviolet protection film
Authors: Hedayati M. K. , Zillohu A. U. , Strunskus T. , Faupel F. , Elbahri M.
Published: January 2014

Plasmonic metamaterials designed for optical frequency have to be shrunk down to few 10th of nanometer which turns their manufacturing cumbersome. Here, we shift the performance of metamaterial down to ultraviolet (UV) by using ultrathin nanocomposite as a tunable plasmonic metamaterial fabricated with tandem co-deposition. It provides the possibility to realize a plasmonic metamaterial absorber for UV frequency with marginal angle sensitivity. Its resonance frequency and intensity can be adjusted by changing thickness and filling factor of the composite. Presented approach for tunable metamaterials for high frequency could pave the way for their application for thermo-photovoltaic, stealth technology, and UV-protective coating.
Pressure induced valence change of Eu in EuFe2As2 at low temperature and high pressures probed by resonant inelastic x-ray scattering
Authors: Kumar Ravhi S. , Zhang Yi , Thamizhavel Arumugam , Svane A. , Vaitheeswaran G. , Kanchana V. , Xiao Yuming , Chow Paul , Chen Changfeng , Zhao Yusheng
Published: January 2014

The effect of pressure on the valence state of Eu in EuFe2As2 has been investigated at high pressures up to 43 GPa at 10 K using resonant inelastic x-ray scattering and x-ray absorption spectroscopy using partial fluorescence yield. Two distinct density functional approaches have been used to complement the experiments. Our experimental results show that the Eu valence increases from a divalent state to a nearly trivalent state under application of pressure in consistence with theoretical simulations. Furthermore, our calculations show that the Eu magnetic moments prevail at high pressure up to 45 GPa.
Magnetic phase transitions and entropy change in layered NdMn1.7Cr0.3Si2
Authors: Md Din M. F. , Wang J. L. , Campbell S. J. , Studer A. J. , Avdeev M. , Kennedy S. J. , Gu Q. F. , Zeng R. , Dou S. X.
Published: January 2014

A giant magnetocaloric effect has been observed around the Curie temperature, TC ∼ 42 K, in NdMn1.7Cr0.3Si2 with no discernible thermal and magnetic hysteresis losses. Below 400 K, three magnetic phase transitions take place around 380 K, 320 K and 42 K. Detailed high resolution synchrotron and neutron powder diffraction (10–400 K) confirmed the magnetic transitions and phases as follows: TNintra ∼ 380 K denotes the transition from paramagnetism to intralayer antiferromagnetism (AFl), TNinter ∼ 320 K represents the transition from the AFl structure to the canted antiferromagnetic spin structure (AFmc), while TC ∼ 42 K denotes the first order magnetic transition from AFmc to canted ferromagnetism (Fmc + F(Nd)) due to ordering of the Mn and Nd sub-lattices. The maximum values of the magnetic entropy change and the adiabatic temperature change, around TC for a field change of 5 T are evaluated to be −ΔSMmax ∼ 15.9 J kg−1 K−1 and ΔTadmax ∼ 5 K, respectively. The first order magnetic transition associated with the low levels of hysteresis losses (thermal <∼0.8 K; magnetic field <∼0.1 T) in NdMn1.7Cr0.3Si2 offers potential as a candidate for magnetic refrigerator applications in the temperature region below 45 K.
Hopping process of bound excitons under an energy gradient
Authors: Jacopin Gwénolé , Shahmohammadi Mehran , Ganière Jean-Daniel , Deveaud Benoît
Published: January 2014

We report on the mechanism of hopping for bound excitons under an energy gradient. By means of a Monte-Carlo simulation, we show that this mechanism explains the movement of bound excitons observed experimentally. We show that the speed of the excitons decreases quickly with temperature. Thanks to an effective medium approximation, we deduce an analytical model to estimate the average speed at T = 0 K. Finally, we compare our simulations results to the speed observed in bent ZnO wires and find a good agreement between theory and experiments.
Growth parameter optimization and interface treatment for enhanced electron mobility in heavily strained GaInAs/AlInAs high electron mobility transistor structures
Authors: Fedoryshyn Yuriy , Ostinelli Olivier , Alt Andreas , Pallin Angel , Bolognesi Colombo R.
Published: January 2014

The optimization of heavily strained Ga0.25In0.75As/Al0.48In0.52As high electron mobility transistor structures is discussed in detail. The growth parameters and the channel layer interfaces were optimized in order to maximize the mobility of the two-dimensional electron gas. Structures composed of an 11 nm thick channel layer and a 4 nm thick spacer layer exhibited electron mobilities as high as 15 100 cm2/Vs and 70 000 cm2/Vs at 300 and 77 K, respectively, for channels including InAs strained layers. The sheet carrier density was kept above 2.5 × 1012 cm−2 throughout the entire study.
Phase transformation between Cu(In,Sn)2 and Cu2(In,Sn) compounds formed on single crystalline Cu substrate during solid state aging
Authors: Tian Feifei , Liu Zhi-Quan , Guo Jingdong
Published: January 2014

Interfacial reactions between eutectic SnIn and single crystalline Cu during solid-state aging at low temperature were investigated systematically. Three types of phase transformations between Cu(In,Sn)2 layer and Cu2(In,Sn) layer were observed, which are Cu(In,Sn)2 grows and Cu2(In,Sn) consumes at 40 °C, Cu(In,Sn)2 and Cu2(In,Sn) grow simultaneously at 60 °C, as well as Cu(In,Sn)2 consumes and Cu2(In,Sn) grows at 80 and 100 °C. According to physicochemical approach, the chemical reactions at Cu/Cu2(In,Sn)/Cu(In,Sn)2/SnIn interfaces were discussed in detail. It was concluded that the diffusion ability of Cu and In atoms dominated different phase transformations. When diffusion constants k1In2 > 8/3k1Cu2 Cu(In,Sn)2 will grow, and if k1Cu2 ≫ k1In2 Cu2(In,Sn) will grow. Both Cu(In,Sn)2 and Cu2(In,Sn) can grow in the condition of k1In2 ≈ k1Cu2. The values of k1Cu2 and k1In2 at different temperatures on (100)Cu and (111)Cu substrate were also calculated or estimated by analyzing the growth kinetics of the compound layers.
Reaction instabilities in Co/Al nanolaminates due to chemical kinetics variation over micron-scales
Authors: Reeves Robert V. , Adams David P.
Published: January 2014

The reaction front dynamics of Co/Al reactive nanolaminates were studied as a function of the initial temperature of the unreacted material. Sample geometries that exhibit stable reaction fronts as well as geometries that present “spinning” reaction front instabilities were investigated at initial temperatures ranging from room temperature to 200 °C. It was found that reactions in samples with small reactant periodicities (<66.4 nm) were stable at all temperatures, reaction in large periodicity samples (≥100 nm) were unstable at all temperatures, and reactions in samples with intermediate periodicities transitioned from unstable behavior to stable behavior with increasing initial temperature. The results suggest that behaviors typical of two types of reaction kinetics are present in unstable reaction fronts: slow, diffusion-limited kinetics in the regions between transverse reaction bands, and a faster mechanism at the leading edge of the transverse bands.
Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect
Authors: Belmeguenai M. , Tuzcuoglu H. , Gabor M. S. , Petrisor T. , Tiusan C. , Zighem F. , Chérif S. M. , Moch P.
Published: January 2014

10 nm and 50 nm Co2FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (Ta), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing Ta, while the uniaxial anisotropy field is nearly unaffected by Ta within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta. Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10−3 and 1.3×10−3 for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively).
Magnetic electron focusing and tuning of the electron current with a pn-junction
Authors: Milovanović S. P. , Ramezani Masir M. , Peeters F. M.
Published: January 2014

Transverse magnetic focusing properties of graphene using a ballistic four terminal structure are investigated. The electric response is obtained using the semiclassical billiard model. The transmission exhibits pronounced peaks as a consequence of skipping orbits at the edge of the structure. When we add a pn-junction between the two probes, snake states along the pn-interface appear. Injected electrons are guided by the pn-interface to one of the leads depending on the value of the applied magnetic field. Oscillations in the resistance are found depending on the amount of particles that end up in each lead.
Observation of polymer optical fiber fuse
Authors: Mizuno Yosuke , Hayashi Neisei , Tanaka Hiroki , Nakamura Kentaro , Todoroki Shin-ichi
Published: January 2014

Although high-transmission-capacity optical fibers are in demand, the problem of the fiber fuse phenomenon needs to be resolved to prevent the destruction of fibers. As polymer optical fibers become more prevalent, clarifying their fuse properties has become important. Here, we experimentally demonstrate a fuse propagation velocity of 21.9 mm/s, which is 1–2 orders of magnitude slower than that in standard silica fibers. The achieved threshold power density and proportionality constant between the propagation velocity and the power density are 1/180 of and 17 times the values for silica fibers, respectively. An oscillatory continuous curve instead of periodic voids is formed after the passage of the fuse. An easy fuse termination method is also presented.
Bias-tunable dual-mode ultraviolet photodetectors for photoelectric tachometer
Authors: Li Xin , Qi Junjie , Zhang Qi , Zhang Yue
Published: January 2014

We report bias-tunable dual-mode ultraviolet (UV) photodetectors based on individual ZnO wires and GaN film hybrid structures and investigated their performance for the photoelectric tachometer. Under UV illumination of 355 nm, by altering the bias, these photodetectors could work in two modes: photodiode and photocell, where the fill factor according to the photovoltaic effect is about 0.41 and the photocell mode reveals a larger sensitivity, as compared to the photodiode mode, which was attributed to the insensitivity of the photocell mode to the depletion layer narrowing under UV irradiance.
Blue photoluminescence enhancement in laser-irradiated 6H-SiC at room temperature
Authors: Wu Yan , Ji Lingfei , Lin Zhenyuan , Jiang Yijian , Zhai Tianrui
Published: January 2014

Blue photoluminescence (PL) of 6H-SiC irradiated by an ultraviolet laser can be observed at room temperature in dark condition. PL spectra with Gaussian fitting curve of the irradiated SiC show that blue luminescence band (∼440 nm) is more pronounced than other bands. The blue PL enhancement is the combined result of the improved shallow N-donor energy level and the unique surface state with Si nanocrystals and graphene/Si composite due to the effect of photon energy input by the short-wavelength laser irradiation. The study can provide a promising route towards the preparation of well-controlled blue photoluminescence material for light-emitting devices.
Synchrotron radiation photoemission study of interfacial electronic structure of HfO2 on In0.53Ga0.47As(001)-4 × 2 from atomic layer deposition
Authors: Pi T. W. , Lin T. D. , Lin H. Y. , Chang Y. C. , Wertheim G. K. , Kwo J. , Hong M.
Published: January 2014

The growth of a passivating layer on a In0.53Ga0.47As(001)-4 × 2 surface by atomic-layer deposition of tetrakis[ethylmethylamino]Hafnium (TEMAHf)) followed by the water pulse was investigated by synchrotron radiation photoemission. The Hf atoms maintain four-fold coordination, both after the initial TEMAHf deposition and the subsequent water pulse. The Hf atoms initially bond to the As dangling bonds of the surface As atom located on the edges of the raised ridges. One EMA ligand is removed in this process. Subsequent water exposure substitutes OH ligand for one or more remaining EMA ligands. These in turn react with TEMAHf to form Hf-O-Hf bonds allowing the hafnium oxides to grow. The surface In atoms on the terrace of the raised ridges were partially removed, but none bonded of the precursor atoms. Correlations between the interfacial electronic structure and the electric performance are discussed.
Ultra-high sensitivity graphene photosensors
Authors: Hsieh Ya-Ping , Yen Chih-Han , Lin Po-Shin , Ma Shao-Wei , Ting Chu-Chi , Wu Chih-I , Hofmann Mario
Published: January 2014

Graphene's advantages for sensor applications are offset by its low electric impedance and consequently low signal-to-noise ratio. We have improved the sensitivity of graphene based photosensors by integrating an energy filtering barrier as an amplifying element. The resulting graphene devices exhibit the highest reported photosensitivity (Ion/Ioff ∼ 4000, gain ∼ 10 A/W) while retaining broad band detection and high speed response. In addition to this unprecedented photosensitivity, the proposed device structure renders the complete graphene photosensitive which enables large scale and flexible photodetectors. The presented approach represents a universal route to enhancing the performance of graphene sensors.
Low beryllium content Zr-based bulk metallic glass composite with plasticity and work hardenability
Authors: Zheng Q. , Du J.
Published: January 2014

A modified Zr-based bulk metallic glass matrix composite Zr47.67Cu40Ti3.66Ni2.66Be6 has been produced by increasing the contents of elements of Zr and Cu with higher Poisson ratio and reducing the contents of Ti, Ni, and Be elements with lower Poisson ratio based on famous metallic glass former Vitreloy 1. A compressive yielding strength of 1804 MPa, fracture strength of 1938 MPa and 3.5% plastic strain was obtained for obtained metallic glass composite. Also, work-hardening behavior was observed during compressive experiment which was ascribed to the interaction of the in situ precipitated CuZr phase and shear bands.
Optical properties of carbon microcoils
Authors: Hikita Muneaki , Cao Li , Lafdi Khalid
Published: January 2014

Carbon microcoils (CMCs) have emerged as versatile material artifacts for a variety of applications due to their helical and spiral structures. Embedded in matrix, CMCs have already been demonstrated for their potential tactile/proximity sensor application. In this study, CMCs were prepared using a conventional chemical vapor deposition method, and then were functionalized with octadecylamine. Upon photoexcitation, the functionalized CMCs exhibited photoluminescence in the visible region, which has never been found before. Similar to carbon based nanoparticles, the photoluminescence of CMCs was attributed to electron-hole radiative recombination after surface passivation. The results suggested that this kind of fluorescent functionalized CMCs might be used as a promising class of optical agents for biological applications.
Origin of attendant phenomena of bipolar resistive switching and negative differential resistance in SrTiO3:Nb/ZnO heterojunctions
Authors: Jia C. H. , Sun X. W. , Li G. Q. , Chen Y. H. , Zhang W. F.
Published: January 2014

Epitaxial ZnO thin films were grown on SrTiO3:Nb (NSTO) substrates by pulsed laser deposition. The NSTO/ZnO heterojunctions exhibit a typical rectification characteristic under a small voltage, while two attendant behaviors of bipolar resistive switching and negative differential resistance appear under a large voltage. The NSTO/ZnO heterojunctions show extremely weak resistance switching hysteresis without applying a forward bias. However, when the forward bias increases to some extent, the hysteresis becomes more and more prominent and negative differential resistance gradually appears. Furthermore, the high resistance state is obtained when sweeping from negative to positive voltage bias, and vice versa. We propose a model for these behaviors at NSTO/ZnO interface, in which the space charge region in ZnO is wide in high resistance state when the interface state is unoccupied, while the space charge region becomes narrower in low resistance state due to Fermi pinning when the interface state is completely occupied, and the low resistance state is remained until electrons are detrapped from the interface state.
High-frequency characterization of thermionic charge transport in silicon-on-insulator nanowire transistors
Authors: Betz A. C. , Barraud S. , Wilmart Q. , Plaçais B. , Jehl X. , Sanquer M. , Gonzalez-Zalba M. F.
Published: January 2014

We report on DC and microwave electrical transport measurements in silicon-on-insulator nano-transistors at low and room temperature. At low source-drain voltage, the DC current and radio frequency response show signs of conductance quantization. We attribute this to Coulomb blockade resulting from barriers formed at the spacer-gate interfaces. We show that at high bias transport occurs thermionically over the highest barrier: Transconductance traces obtained from microwave scattering-parameter measurements at liquid helium and room temperature are accurately fitted by a thermionic model. From the fits we deduce the ratio of gate capacitance and quantum capacitance, as well as the electron temperature.
Broadband and wide-angle negative reflection at a phononic crystal boundary
Authors: Zhao Degang , Ye Yangtao , Xu Shengjun , Zhu Xuefeng , Yi Lin
Published: January 2014

We have theoretically and experimentally demonstrated the anomalous negative reflection at the boundary of a well-designed two-dimensional phononic crystal. This exotic phenomenon is attributed to the selective enhancement of −1st order diffraction mode with the zero-order diffraction mode being dramatically suppressed. After material and structural optimization, the negative reflection can be maintained in a broadband of frequencies and for a wide incident angle range. Our system can be employed to design Littrow configuration to realize perfect broadband and wide-angle blazing. The study gives a possibility to achieve greater flexibility and stronger effects in manipulating reflected acoustic waves, which has potential applications in underwater communication, medical ultrasonics, etc.
Investigation of electric field threshold of GaAs photoconductive semiconductor switch triggered by 1.6 μJ laser diode
Authors: Shi Wei , Jiang Huan , Li Mengxia , Ma Cheng , Gui Huaimeng , Wang Luyi , Xue Pengbo , Fu Zhanglong , Cao Juncheng
Published: January 2014

A 3-mm-gapped GaAs photoconductive semiconductor switch is triggered by a 1.6 μJ laser diode. Effects of the rectangular spot's layout and the triggering position on the electric field threshold of nonlinear mode are investigated. As the illuminated position moves from the cathode to the anode, the effective illumination optical energy varies. In that case, when the rectangular spot is perpendicular to two electrodes the electric field threshold increases linearly. And when the rectangular spot is parallel to the electrodes, the electric field threshold exhibits an asymmetric parabola-like curve.
Beam-induced graphitic carbon cage transformation from sumanene aggregates
Authors: Fujita Jun-ichi , Tachi Masashi , Murakami Katsuhisa , Sakurai Hidehiro , Morita Yuki , Higashibayashi Shuhei , Takeguchi Masaki
Published: January 2014

We found that electron-beam irradiation of sumanene aggregates strongly enhanced their transformation into a graphitic carbon cage, having a diameter of about 20 nm. The threshold electron dose was about 32 mC/cm2 at 200 keV, but the transformation is still induced at 20 keV. The transformation sequence suggested that the cage was constructed accompanied by the dynamical movement of the transiently linked sumanene molecules in order to pile up inside the shell. Thus, bond excitation in the sumanene molecules rather than a knock-on of carbon atoms seems to be the main cause of the cage transformation.
Electrical conduction in nanodomains in congruent lithium tantalate single crystal
Authors: Cho Yasuo
Published: January 2014

The electrical current flow behavior was investigated for nanodomains formed in a thin congruent lithium tantalate (LiTaO3) single-crystal plate. When the nanodomains were relatively large, with diameters of about 100 nm, current flow was detected along the domain wall. However, when they were about 40 nm or smaller, the current flowed through the entire nanodomain. Schottky-like rectifying behavior was observed. Unlike the case of LiNbO3, optical illumination was not required for current conduction in LiTaO3. A clear temperature dependence of the current was found indicating that the conduction mechanism for nanodomains in LiTaO3 may involve thermally activated carrier hopping.
Nanofocusing of mid-infrared electromagnetic waves on graphene monolayer
Authors: Qiu Weibin , Liu Xianhe , Zhao Jing , He Shuhong , Ma Yuhui , Wang Jia-Xian , Pan Jiaoqing
Published: January 2014

Nanofocusing of mid-infrared (MIR) electromagnetic waves on graphene monolayer with gradient chemical potential is investigated with numerical simulation. On an isolated freestanding monolayer graphene sheet with spatially varied chemical potential, the focusing spot sizes of frequencies between 44 THz and 56 THz can reach around 1.6 nm and the intensity enhancement factors are between 2178 and 654. For 56 THz infrared, a group velocity as slow as 5×10−5 times of the light speed in vacuum is obtained at the focusing point. When the graphene sheet is placed on top of an aluminum oxide substrate, the focusing spot size of 56 THz infrared reduces to 1.1 nm and the intensity enhancement factor is still as high as 220. This structure offers an approach for focusing light in the MIR regime beyond the diffraction limit without complicated device geometry engineering.
Policy Transformations and Translations: Lessons for Sustainable Water Management in Peri-Urban Delhi, India
Authors: Randhawa Pritpal , Marshall Fiona
Published: January 2014

This paper explores the complex interactions that occur as formal policies are interpreted and utilised to develop water management plans in peri-urban Delhi. With an emphasis on people's participation in decision making, the paper examines some of the disjunctures between formal assumptions about water management in peri-urban areas and practices on the ground. In doing so it attempts to reveal some of the key processes responsible for social fragmentation of services. The paper describes informal coping strategies adopted by poor and marginalised peri-urban communities with little or no access to formal provision. Within this, the role of ‘hidden’ interactions with the formal system are highlighted in the context of failures of formal participatory platforms. The paper argues that enhanced understanding of the policy process, and the alternative arrangements that emerge in response to its shortfalls, could be important contributory factors in identifying realistic intervention strategies for enhanced, more socially just, water management in peri-urban situations.
Effect of Extended Conjugation on the Optoelectronic Properties of Benzo[1,2-d:4,5-d′]bisoxazole Polymers
Authors: Tlach Brian C. , Tomlinson Aimée L. , Morgan Kiley D. , Collins Christopher R. , Zenner Michael D. , Jeffries-EL Malika
Published: January 2014

Four copolymers comprising benzo[1,2-d:4,5-d']bisoxazole (BBO) and benzo[1,2-b:4,5-b′]dithiophene (BDT) bearing phenylethynyl substituents on either the BBO, BDT moieties or both units were synthesised and the influence of two-dimensional conjugation on their optoelectronic properties investigated. Extending conjugation along the BBO resulted in a 0.5 eV decrease in the LUMO level, whereas the HOMO level was raised by 0.2 eV. Extending conjugation across the BDT moiety in also resulted in a 0.5 eV decrease in the LUMO level, however, the effect was negligible on the HOMO level. Thus, cross-conjugation can be used to independently tune the LUMO level within these systems.
DABCO Promoted Regioselective Synthesis of New Diversely Functionalized 3-Hydroxy-2-Oxindole Scaffolds
Authors: Thakur Pramod B. , Nanubolu Jagdeesh B. , Meshram Harshadas M.
Published: January 2014

An efficient and highly regioselective γ-addition of β-keto sulfones on isatins has been achieved in the presence of a catalytic amount of 1,4-diazabicyclo[2.2.2]octane (DABCO) to afford a γ-(3-hydroxy-2-oxindole)-β-keto sulfone structural framework. The scope of the method is tested by screening a series of isatin electrophiles as well as β-keto sulfones. The described method was found to be very handy and provides straightforward access for the diversely functionalized 3-β-keto sulfone substituted-3-hydroxy-2-oxindole structural scaffolds in very good yields from readily available starting materials under metal-free reaction conditions.
Myosin-binding protein C displaces tropomyosin to activate cardiac thin filaments and governs their speed by an independent mechanism
Authors: Mun Ji Young , Previs Michael J. , Yu Hope Y. , Gulick James , Tobacman Larry S. , Beck Previs Samantha , Robbins Jeffrey , Warshaw David M. , Craig Roger
Published: January 2014

Significance

Myosin-binding protein C (MyBP-C) is a component of myosin filaments, one of the two sets of contractile elements whose relative sliding is the basis of muscle contraction. In the heart, MyBP-C modulates contractility in response to cardiac stimulation; mutations in MyBP-C lead to cardiac disease. The mechanism by which MyBP-C modulates cardiac contraction is not understood. Using electron microscopy and a light microscopic assay for filament sliding, we demonstrate that MyBP-C binds to the other set of filaments, containing actin and the regulatory component, tropomyosin. In so doing, it displaces tropomyosin from its inhibitory position to activate actin filament interaction with myosin, promoting filament sliding. These findings provide insights into the molecular basis of heart function.