bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid model for throughput evaluation of orthogonal frequency division multiple access networks
Authors: Mahato Shyam Babu , Van Do Tien , Allen Ben , Liu Enjie , Zhang Jie
Published: September 2014

Data throughput is an important metric used in the performance evaluation of the next generation cellular networks such as long‐term evolution (LTE) and LTE‐advanced. To evaluate the performance of these networks, Monte Carlo simulation schemes are usually used. Such simulations do not provide the throughput of intermediate call state; instead it gives the overall performance of this network. The authors propose a hybrid model consisting of both analysis and simulation. The benefit of this model is that the throughput of any possible call state in the system can be evaluated. Here, the probability of possible call distribution is first obtained by analysis, which is used as input to the event‐driven‐based simulator to calculate the throughput of a call state. Comparison is made between throughput obtained from the author's hybrid model with that obtained from event‐driven‐based simulation. Numerical results are presented and show good agreement between both the proposed hybrid model and the simulation. The maximum difference of relative throughput between their hybrid model and the simulation is found in the interval of (0.04 and 1.06%) over a range of call arrival rates, mean holding times and number of resource blocks in the system.
Improved dual sided doped memristor: modelling and applications
Authors: Shrivastava Anup , Khalid Muhammad , Singh Komal , Singh Jawar
Published: September 2014

Memristor as a novel and emerging electronic device having vast range of applications suffer from poor frequency response and saturation length. In this paper, the authors present a novel and an innovative device structure for the memristor with two active layers and its non‐linear ionic drift model for an improved frequency response and saturation length. The authors investigated and compared the I–V characteristics for the proposed model with the conventional memristors and found better results in each case (different window functions) for the proposed dual sided doped memristor. For circuit level simulation, they developed a SPICE model of the proposed memristor and designed some logic gates based on hybrid complementary metal oxide semiconductor memristive logic (memristor ratioed logic). The proposed memristor yields improved results in terms of noise margin, delay time and dynamic hazards than that of the conventional memristors (single active layer memristors).
Low‐power adiabatic 9T static random access memory
Authors: Takahashi Yasuhiro , Nayan Nazrul Anuar , Sekine Toshikazu , Yokoyama Michio
Published: September 2014

In this paper, the authors propose a novel static random access memory (SRAM) that employs the adiabatic logic principle. To reduce energy dissipation, the proposed adiabatic SRAM is driven by two trapezoidal‐wave pulses. The cell structure of the proposed SRAM has two high‐value resistors based on a p‐type metal‐oxide semiconductor transistor, a cross‐coupled n‐type metal‐oxide semiconductor (NMOS) pair and an NMOS switch to reduce the short‐circuit current. The inclusion of a transmission‐gate controlled by a write word line signal allows the proposed circuit to operate as an adiabatic SRAM during data writing. Simulation results show that the energy dissipation of the proposed SRAM is lower than that of a conventional adiabatic SRAM.
Exploring older driver crash trend: New Jersey case study
Authors: Trieu Vanvi , Park Seri , McFadden John
Published: September 2014

Older drivers age 65 and above are known to experience greater risk on the roadway as well as increasing the risk to other roadway users. Within the next 20 years, their population is expected to increase from 41 million in 2011 to 70 million in 2030. To address this foreseeable change, the nation's recent Moving Ahead for Progress in the 21st Century (MAP‐21) act requires state and local governments to examine older drivers and pedestrian risks and implement countermeasures as appropriate. This research was conducted to assist agencies in strategising for future plans, programmes and initiatives to better address the problem presented. This was accomplished by performing a detailed engineering analysis on crash data of older drivers over a 10‐year period (2003–2012) from the state of New Jersey to identify crash trends and characteristics. A major finding from this research was the increase in fatal crashes of older drivers as a function of age. Top‐ranking collision types with other vehicles and non‐vehicles were identified. Crashes as a function of seasonal change, climate and lighting conditions were also examined.
CMOS time‐to‐digital converters for mixed‐mode signal processing
Authors: Yuan Fei
Published: September 2014

This study provides an in‐depth review of the principles, architectures and design techniques of CMOS time‐to‐digital converters (TDCs). The classification of TDCs is introduced. It is followed by the examination of the parameters quantifying the performance of TDCs. Sampling TDCs including direct‐counter TDCs, tapped delay‐line TDCs, pulse‐shrinking delay‐line TDCs, cyclic pulse‐shrinking TDCs, direct‐counter TDCs with interpolation, vernier TDCs, flash TDCs, successive approximation TDCs and pipelined TDCs are studied and their pros and cons are compared. Noise‐shaping TDCs that reduce in‐band noise below technology limit are investigated. These TDCs include gated ring oscillator TDCs, switched ring oscillator TDCs, relaxation oscillator TDCs, ΔΣ TDCs and MASH TDCs. The performance of sampling and noise‐shaping TDCs is compared. The direction of future research on TDCs is explored.
Sensorless speed control of a five‐phase induction machine under open‐phase condition
Authors: Morsy Ahmed S. , Abdelkhalik Ayman S. , Ahmed Shehab , Massoud Ahmed Mohamed
Published: September 2014

Recently, multiphase machines have been promoted as competitors to their three‐phase counterparts in high‐power safety‐critical drive applications. Among numerous advantages of multiphase induction machine (IM) drives, self‐starting and operation under open phase(s) stand as the most salient features. With open phase(s), optimal current control provides disturbance‐ free operation given a set of objective functions. Although hysteresis current control was merely employed in the literature as it offers a simple controller structure to control the remaining healthy phases, it is not suitable for high‐power applications. In the literature, multiple synchronous reference frame (dq) control can be an alternative; however, it requires back and forth transformations with several calculations and additional sophistication. In this paper, a simple technique employing adaptive proportional resonant (PR) current controllers is presented to control a five‐phase IM under open‐phase conditions. Results for both volt/hertz (V/f) and field oriented control (FOC) systems are presented. Moreover, sensorless operation under fault condition is also demonstrated by estimating the machine speed using a rotor flux‐based model reference adaptive system (MRAS) speed estimator. The proposed controllers are experimentally verified and compared. Although FOC provides better dynamic performance, V/f control offers a simpler control structure and a lower number of PR controllers.
Survey of buffer management policies for delay tolerant networks
Authors: Jain Sweta , Chawla Meenu
Published: September 2014

Delay tolerant networks (DTN) are a class of networks that are a subset of the traditional mobile ad‐hoc networks. It differs from mobile ad hoc networks (MANETs) in the sense that it can withstand high delays in delivering data because of frequent network partitions, limited bandwidth and storage constraints persisting in such networks. Owing to these inherent characteristics of the delay tolerant networks improving delivery ratio in such networks depends on two main factors‐use of routing strategy and a good buffer management policy. Many routing protocols have been proposed in the literature for DTN. Buffer management is a very important factor in DTN because of the very limited buffer space available in DTN nodes. Although a scheduling policy in DTN determines which message has to be forwarded first, the dropping policy decides which messages are to be dropped in case of buffer overflow. This Letter presents a survey of the existing buffer management policies proposed for DTN and discusses the pros and cons of these approaches. The buffer management techniques have been classified on the basis of information used by them whether they are based on local information of messages available at the node or global information of all the messages in the network.
Ensemble unscented Kalman filter for state inference in continuous–discrete systems
Authors: Liu Bin
Published: September 2014

The authors consider non‐linear state filtering problem in continuous–discrete systems, where the system dynamics is modelled by a stochastic differential equation, and noisy measurements of the system are obtained at discrete time instances. A novel particle method is proposed based on sequential importance sampling. This approach uses a bank of the continuous–discrete unscented Kalman filters (CDUKFs) to obtain the importance proposal distribution, retaining the advantage of the CDUKF in continuous–discrete systems as well as the accuracy of particle filter in highly non‐linear systems. Simulation results show that the algorithm outperforms some other benchmarks substantially in estimation accuracy.
Spectral estimation for long‐term evolution transceivers using low‐complex filter banks
Authors: Schlechter Thomas , Juritsch Christoph , Huemer Mario
Published: September 2014

For mobile user equipments (UEs), a careful power management is essential. Despite this fact, quite an amount of energy is wasted in today's UEs’ analogue (AFEs) and digital frontends (DFEs). These are engineered for extracting the wanted signal from a spectral environment defined in the corresponding communication standards with their extremely tough requirements. These requirements define a worst‐case scenario still ensuring reliable communication. In a typical receiving process the actual requirements can be considered as less critical. Knowledge about the actual environmental spectral conditions allows to reconfigure both frontends to the actual needs and to save energy. In this paper, the authors present a highly efficient generic spectrum sensing approach, which allows to collect information about the actual spectral environment of an UE. This information can be used to reconfigure both the AFE and DFE, thus endowing them with increased intelligence. A low‐complex multiplier free filter bank extended by an efficient power calculation unit will be introduced. They also present simulation results, which illustrate the performance of the spectrum sensing approach and a complexity comparison with different well‐known implementations is given. Furthermore, estimates on the chip area and power consumption based on a 65 nm CMOS technology database are provided, considering the Smarti4G chip as a reference.
Investigation of wound rotor induction machine vibration signal under stator electrical fault conditions
Authors: Djurović Sinisa , Vilchis‐Rodriguez Damian S. , Smith Alexander Charles
Published: September 2014

This paper investigates wound rotor induction machine torque and vibration signals spectra for operation with and without a stator short‐circuit or open‐circuit winding fault. Analytical expressions that enable the healthy and faulty machine pulsating electromagnetic torque frequencies to be related to shaft speed are derived and validated for operating conditions of interest. A coupled‐circuit machine model is used to investigate the healthy and faulty electromagnetic torque signal. Shaft torque and stator frame vibration are measured on a laboratory test rig comprising a 30 kW wound rotor induction machine. It is shown that the existence of a stator winding inherent electrical unbalance or that arising from fault gives rise to a range of pulsating torque frequencies that are transmitted to the machine frame and can be detected in the measured vibration signal. The magnitudes of the resulting vibration components are demonstrated to be largely determined by the unbalance severity and the mechanical system response. The presented experimental results clearly validate the analytical and simulation analysis for the operating range of the investigated industrial machine design.
Two-dimensional and three-dimensional Coulomb clusters in parabolic traps
Authors: D'yachkov L. G. , Myasnikov M. I. , Petrov O. F. , Hyde T. W. , Kong J. , Matthews L.
Published: September 2014

We consider the shell structure of Coulomb clusters in an axially symmetric parabolic trap exhibiting a confining potential Uc(ρ,z)=(mω2/2)(ρ2+αz2). Assuming an anisotropic parameter α = 4 (corresponding to experiments employing a cusp magnetic trap under microgravity conditions), we have calculated cluster configurations for particle numbers N = 3 to 30. We have shown that clusters with N ≤ 12 initially remain flat, transitioning to three-dimensional configurations as N increases. For N = 8, we have calculated the configurations of minimal potential energy for all values of α and found the points of configuration transitions. For N = 13 and 23, we discuss the influence of both the shielding and anisotropic parameter on potential energy, cluster size, and shell structure.
Effects of truncating van der Waals interactions in lipid bilayer simulations
Authors: Huang Kun , García Angel E.
Published: September 2014

In membrane simulations, it is known that truncating electrostatic interactions results in artificial ordering of lipids at the truncation distance. However, less attention has been paid to the effect of truncating van der Waals (VDW) interactions. Since the VDW potential decays as r−6, it is frequently neglected beyond a cutoff of around 1 nm. In some cases, analytical dispersion corrections appropriate for isotropic systems are applied to the pressure and the potential energy. In this work, we systematically study the effect of truncating VDW interactions at different cutoffs in 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine bilayers with the Berger force field. We show that the area per lipid decreases systematically when the VDW cutoff (rc) increases. This dependence persists even when dispersion corrections are applied. Since the analytical form of the dispersion correction is only appropriate for isotropic systems, we suggest that a long VDW cutoff should be used in preference over a short VDW cutoff. To determine the appropriate cutoff, we simulate liquid pentadecane with the Berger parameters and find that rc ≥ 1.4 nm is sufficient to reproduce the density and the heat of vaporization of pentadecane. Bilayers simulated with rc ≥ 1.4 nm show an improved agreement with experiments in both the form factors and the deuterium order parameters. Finally, we report that the VDW cutoff has a significant impact on the lipid flip-flop energetics and an inappropriate short VDW cutoff results in a bilayer that is prone to form water defects across the bilayer.
Note: On the generation of sub-300 keV flash-X-rays using rod-pinch diode: An experimental investigation
Authors: Satyanarayana N. , Rajawat R. K. , Basu Shibaji , Rao A. Durga Prasad , Mittal K. C.
Published: September 2014

Generation of flash X-rays (FXRs) at less than 500 keV is described with emphasis on experimental investigation. The pulser is a Tesla transformer-Water transmission line based pulsed power generator operating in double resonance mode to power a rod-pinch diode. The configuration of aspect ratio reported here falls much below the normally reported ratios for the rod-pinch diode operation. Experimental investigation at such low pulsed voltage has revealed “flowering” of the anode tip and “pitting” of the perspex window. A possible explanation in terms of Lorentz body force is discussed rather than the pinch mechanism generally suggested in literature. The experimental investigation for the FXR generation is corroborated by measuring the radiation dose using CaSO4 (Dy) thermo luminescent dosimeters.
High-Q silicon photonic crystal cavity for enhanced optical nonlinearities
Authors: Dharanipathy Ulagalandha Perumal , Minkov Momchil , Tonin Mario , Savona Vincenzo , Houdré Romuald
Published: September 2014

We fabricate and experimentally characterize an H0 photonic crystal slab nanocavity with a design optimized for maximal quality factor, Q = 1.7 × 106. The cavity, fabricated from a silicon slab, has a resonant mode at λ = 1.59 μm and a measured Q-factor of 400 000. It displays nonlinear effects, including high-contrast optical bistability, at a threshold power among the lowest ever reported for a silicon device. With a theoretical modal volume as small as V = 0.34(λ/n)3, this cavity ranks among those with the highest Q/V ratios ever demonstrated, while having a small footprint suited for integration in photonic circuits.
Nanothermodynamics of large iron clusters by means of a flat histogram Monte Carlo method
Authors: Basire M. , Soudan J.-M. , Angelié C.
Published: September 2014

The thermodynamics of iron clusters of various sizes, from 76 to 2452 atoms, typical of the catalyst particles used for carbon nanotubes growth, has been explored by a flat histogram Monte Carlo (MC) algorithm (called the σ-mapping), developed by Soudan et al. [J. Chem. Phys. 135, 144109 (2011), Paper I]. This method provides the classical density of states, gp(Ep) in the configurational space, in terms of the potential energy of the system, with good and well controlled convergence properties, particularly in the melting phase transition zone which is of interest in this work. To describe the system, an iron potential has been implemented, called “corrected EAM” (cEAM), which approximates the MEAM potential of Lee et al. [Phys. Rev. B 64, 184102 (2001)] with an accuracy better than 3 meV/at, and a five times larger computational speed. The main simplification concerns the angular dependence of the potential, with a small impact on accuracy, while the screening coefficients Sij are exactly computed with a fast algorithm. With this potential, ergodic explorations of the clusters can be performed efficiently in a reasonable computing time, at least in the upper half of the solid zone and above. Problems of ergodicity exist in the lower half of the solid zone but routes to overcome them are discussed. The solid-liquid (melting) phase transition temperature Tm is plotted in terms of the cluster atom number Nat. The standard \documentclass[12pt]{minimal}\begin{document}$N_{at}^{-1/3}$\end{document}Nat−1/3 linear dependence (Pawlow law) is observed for Nat >300, allowing an extrapolation up to the bulk metal at 1940 ±50 K. For Nat <150, a strong divergence is observed compared to the Pawlow law. The melting transition, which begins at the surface, is stated by a Lindemann-Berry index and an atomic density analysis. Several new features are obtained for the thermodynamics of cEAM clusters, compared to the Rydberg pair potential clusters studied in Paper I.
A combined kick-out and dissociative diffusion mechanism of grown-in Be in InGaAs and InGaAsP. A new finite difference-Bairstow method for solution of the diffusion equations
Authors: Koumetz Serge D. , Martin Patrick , Murray Hugues
Published: September 2014

Experimental results on the diffusion of grown-in beryllium (Be) in indium gallium arsenide (In0.53Ga0.47As) and indium gallium arsenide phosphide (In0.73Ga0.27As0.58P0.42) gas source molecular beam epitaxy alloys lattice-matched to indium phosphide (InP) can be successfully explained in terms of a combined kick-out and dissociative diffusion mechanism, involving neutral Be interstitials (Bei0), singly positively charged gallium (Ga), indium (In) self-interstitials (IIII+) and singly positively charged Ga, In vacancies (VIII+). A new numerical method of solution to the system of diffusion equations, based on the finite difference approximations and Bairstow's method, is proposed.
Water and formic acid aggregates: A molecular dynamics study
Authors: Vardanega Delphine , Picaud Sylvain
Published: September 2014

Water adsorption around a formic acid aggregate has been studied by means of molecular dynamics simulations in a large temperature range including tropospheric conditions. Systems of different water contents have been considered and a large number of simulations has allowed us to determine the behavior of the corresponding binary formic acid–water systems as a function of temperature and humidity. The results clearly evidence a threshold temperature below which the system consists of water molecules adsorbed on a large formic acid grain. Above this temperature, formation of liquid-like mixed aggregates is obtained. This threshold temperature depends on the water content and may influence the ability of formic acid grains to act as cloud condensation nuclei in the Troposphere.
Onsager's symmetry relation and the residual parallel Reynolds stress in a magnetized plasma with electrostatic turbulence
Authors: Zuo Yang , Wang Shaojie
Published: September 2014

The physics of the residual parallel Reynolds stress in a rotating plasma with electrostatic turbulence is explicitly identified by using the transport formulation of the gyrokinetic turbulence. It is clarified that the residual stress consists of four terms, among which are the cross terms due to the pressure gradient and the temperature gradient and the terms related to the turbulent acceleration impulse and the turbulent heating rate. The last two terms are identified for the first time, and are shown to cause analogous residual term in the heat flux. Meanwhile, the transport matrix reveals diffusion in the phase space. The transport matrix is demonstrated to satisfy the Onsager's symmetry relation.
The decay rate of solution for the bipolar Navier-Stokes-Poisson system
Authors: Wang Weike , Xu Xin
Published: September 2014

In this paper, the Cauchy problem for the bipolar Navier-Stokes-Poisson system is studied. We obtain the global existence and the Hs decay rate of classical solutions for this problem. Our approach is mainly based on the analysis of the Green's function of the linearized system and some elaborate energy estimates. It should be mentioned that with the help of long wave-short wave decomposition, the decay rate of the higher order derivatives of the solutions is obtained. Furthermore, based on the Hs decay rate of the solutions, we also give the Lp estimate of the solution.
Analytic first derivatives for a spin-adapted open-shell coupled cluster theory: Evaluation of first-order electrical properties
Authors: Datta Dipayan , Gauss Jürgen
Published: September 2014

An analytic scheme is presented for the evaluation of first derivatives of the energy for a unitary group based spin-adapted coupled cluster (CC) theory, namely, the combinatoric open-shell CC (COSCC) approach within the singles and doubles approximation. The widely used Lagrange multiplier approach is employed for the derivation of an analytical expression for the first derivative of the energy, which in combination with the well-established density-matrix formulation, is used for the computation of first-order electrical properties. Derivations of the spin-adapted lambda equations for determining the Lagrange multipliers and the expressions for the spin-free effective density matrices for the COSCC approach are presented. Orbital-relaxation effects due to the electric-field perturbation are treated via the Z-vector technique. We present calculations of the dipole moments for a number of doublet radicals in their ground states using restricted open-shell Hartree-Fock (ROHF) and quasi-restricted HF (QRHF) orbitals in order to demonstrate the applicability of our analytic scheme for computing energy derivatives. We also report calculations of the chlorine electric-field gradients and nuclear quadrupole-coupling constants for the CCl, CH2Cl, ClO2, and SiCl radicals.
Fabrication of AlN/BN bishell hollow nanofibers by electrospinning and atomic layer deposition
Authors: Haider Ali , Ozgit-Akgun Cagla , Kayaci Fatma , Okyay Ali Kemal , Uyar Tamer , Biyikli Necmi
Published: September 2014

Aluminum nitride (AlN)/boron nitride (BN) bishell hollow nanofibers (HNFs) have been fabricated by successive atomic layer deposition (ALD) of AlN and sequential chemical vapor deposition (CVD) of BN on electrospun polymeric nanofibrous template. A four-step fabrication process was utilized: (i) fabrication of polymeric (nylon 6,6) nanofibers via electrospinning, (ii) hollow cathode plasma-assisted ALD of AlN at 100 °C onto electrospun polymeric nanofibers, (iii) calcination at 500 °C for 2 h in order to remove the polymeric template, and (iv) sequential CVD growth of BN at 450 °C. AlN/BN HNFs have been characterized for their chemical composition, surface morphology, crystal structure, and internal nanostructure using X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction. Measurements confirmed the presence of crystalline hexagonal BN and AlN within the three dimensional (3D) network of bishell HNFs with relatively low impurity content. In contrast to the smooth surface of the inner AlN layer, outer BN coating showed a highly rough 3D morphology in the form of BN nano-needle crystallites. It is shown that the combination of electrospinning and plasma-assisted low-temperature ALD/CVD can produce highly controlled multi-layered bishell nitride ceramic hollow nanostructures. While electrospinning enables easy fabrication of nanofibrous template, self-limiting reactions of plasma-assisted ALD and sequential CVD provide control over the wall thicknesses of AlN and BN layers with sub-nanometer accuracy.
Dispersion of the linear and nonlinear optical susceptibilities of the CuAl(S1−xSex)2 mixed chaclcopyrite compounds
Authors: Reshak A. H. , Brik M. G. , Auluck S.
Published: September 2014

Based on the electronic band structure, we have calculated the dispersion of the linear and nonlinear optical susceptibilities for the mixed CuAl(S1−xSex)2 chaclcopyrite compounds with x = 0.0, 0.25, 0.5, 0.75, and 1.0. Calculations are performed within the Perdew-Becke-Ernzerhof general gradient approximation. The investigated compounds possess a direct band gap of about 2.2 eV (CuAlS2), 1.9 eV (CuAl(S0.75Se0.25)2), 1.7 eV (CuAl(S0.5Se0.5)2), 1.5 eV (CuAl(S0.25Se0.75)2), and 1.4 eV (CuAlSe2) which tuned to make them optically active for the optoelectronics and photovoltaic applications. These results confirm that substituting S by Se causes significant band gaps' reduction. The optical function's dispersion ε2xx(ω) and ε2zz(ω)/ε2xx(ω), ε2yy(ω), and ε2zz(ω) was calculated and discussed in detail. To demonstrate the effect of substituting S by Se on the complex second-order nonlinear optical susceptibility tensors, we performed detailed calculations for the complex second-order nonlinear optical susceptibility tensors, which show that the neat parents compounds CuAlS2 and CuAlSe2 exhibit |χ123(2)(−2ω;ω;ω)| as the dominant component, while the mixed alloys exhibit |χ111(2)(−2ω;ω;ω)| as the dominant component. The features of |χ123(2)(−2ω;ω;ω)| and |χ111(2)(−2ω;ω;ω)| spectra were analyzed on the basis of the absorptive part of the corresponding dielectric function ε2(ω) as a function of both ω/2 and ω.
Adsorbing H2S onto a single graphene sheet: A possible gas sensor
Authors: Reshak A. H. , Auluck S.
Published: September 2014

The electronic structure of pristine graphene sheet and the resulting structure of adsorbing a single molecule of H2S on pristine graphene in three different sites (bridge, top, and hollow) are studied using the full potential linearized augmented plane wave method. Our calculations show that the adsorption of H2S molecule on the bridge site opens up a small direct energy gap of about 0.1 eV at symmetry point M, while adsorption of H2S on top site opens a gap of 0.3 eV around the symmetry point K. We find that adsorbed H2S onto the hollow site of pristine graphene sheet causes to push the conduction band minimum and the valence band maximum towards Fermi level resulting in a metallic behavior. Comparing the angular momentum decomposition of the atoms projected electronic density of states of pristine graphene sheet with that of H2S–graphene for three different cases, we find a significant influence of the location of the H2S molecule on the electronic properties especially the strong hybridization between H2S molecule and graphene sheet.
Observation of heavy- and light-hole split direct bandgap photoluminescence from tensile-strained GeSn (0.03% Sn)
Authors: Harris Thomas R. , Yeo Yung Kee , Ryu Mee-Yi , Beeler Richard T. , Kouvetakis John
Published: September 2014

Temperature- (T-) and laser power-dependent photoluminescence (PL) measurements have been made for the tensile-strained, undoped GeSn (0.03% Sn) film grown on Si substrate. The PL results show not only clear strain-split direct bandgap transitions to the light-hole (LH) and heavy-hole (HH) bands at energies of 0.827 and 0.851 eV at 10 K, respectively, but also clearly show both strong direct and indirect bandgap related PL emissions at almost all temperatures, which are rarely observed. This split of PL emissions can be directly observed only at low T and moderate laser power, and the two PL peaks merge into one broad PL peak at room temperature, which is mainly due to the HH PL emission rather than LH transition. The evolution of T-dependent PL results also clearly show the competitive nature between the direct and indirect bandgap related PL transitions as T changes. The PL analysis also indicates that the energy gap reduction in Γ valley could be larger, whereas the bandgap reduction in L valley could be smaller than the theory predicted. As a result, the separation energy between Γ and L valleys (∼86 meV at 300 K) is smaller than theory predicted (125 meV) for this Ge-like sample, which is mainly due to the tensile strain. This finding strongly suggests that the indirect-to-direct bandgap transition of Ge1−ySny could be achieved at much lower Sn concentration than originally anticipated if one utilizes the tensile strain properly. Thus, Ge1−ySny alloys could be attractive materials for the fabrication of direct bandgap Si-based light emitting devices.
The fate of the 2√3 × 2√3R(30°) silicene phase on Ag(111)
Authors: Liu Zhi-Long , Wang Mei-Xiao , Liu Canhua , Jia Jin-Feng , Vogt Patrick , Quaresima Claudio , Ottaviani Carlo , Olivieri Bruno , De Padova Paola , Lay Guy Le
Published: September 2014

Silicon atoms deposited on Ag(111) produce various single layer silicene sheets with different buckling patterns and periodicities. Low temperature scanning tunneling microscopy reveals that one of the silicene sheets, the hypothetical √7 × √7 silicene structure, on 2√3 × 2√3 Ag(111), is inherently highly defective and displays no long-range order. Moreover, Auger and photoelectron spectroscopy measurements reveal its sudden death, to end, in a dynamic fating process at ∼300 °C. This result clarifies the real nature of the 2√3 × 2√3R(30°) silicene phase and thus helps to understand the diversity of the silicene sheets grown on Ag(111).
Stability of graphene doping with MoO3 and I2
Authors: D'Arsié Lorenzo , Esconjauregui Santiago , Weatherup Robert , Guo Yuzheng , Bhardwaj Sunil , Centeno Alba , Zurutuza Amaia , Cepek Cinzia , Robertson John
Published: September 2014

We dope graphene by evaporation of MoO3 or by solution-deposition of I2 and assess the doping stability for its use as transparent electrodes. Electrical measurements show that both dopants increase the graphene sheet conductivity and find that MoO3-doped graphene is significantly more stable during thermal cycling. Raman spectroscopy finds that neither dopant creates defects in the graphene lattice. In-situ photoemission determines the minimum necessary thickness of MoO3 for full graphene doping.
Effect of silver doping on the surface of La5/8Ca3/8MnO3 epitaxial films
Authors: Tselev A. , Vasudevan R. K. , Kalinin S. V. , Baddorf A. P.
Published: September 2014

Thin film manganese oxides (manganites) display remarkable properties, such as colossal magnetoresistance and charge ordered phases, and became a focal point of research in the past two decades owing to potential applications ranging from oxide spintronics to resistive switching-based memories. LaxCa1−xMnO3 (LCMO), a widely studied manganite, is known to substantially improve its transport properties when doped with Ag. However, despite the abundance of studies on LCMO, the effect of silver on the surface structure is unknown. Here, through in-situ methods, scanning tunneling microscopy (STM) is performed on La5/8Ca3/8MnO3 films grown by pulsed laser deposition. Films doped by silver, as confirmed by in-situ X-ray photoelectron spectroscopy, display large-scale reconstructions, interpreted as being of type (√10 × √10)R18.4°, while films lacking silver display a (√2 × √2)R45° reconstruction that may be associated with a surface charge-ordered state. It is posited that the possible cause of the varied reconstructions is due to a vacancy ordering on top of the existing (√2 × √2)R45° reconstruction. These studies highlight the influence of Ag on the surface structure, and therefore a route towards modifying the surface properties of manganites.
Improved study of electric dipoles on the Si(100)-2 × 1 surface by non-contact scanning nonlinear dielectric microscopy
Authors: Suzuki Masataka , Yamasue Kohei , Abe Masayuki , Sugimoto Yoshiaki , Cho Yasuo
Published: September 2014

We studied a Si(100)-2 × 1 surface by non-contact scanning nonlinear dielectric microscopy (NC-SNDM). Simultaneously taken images of the topography and electric dipole moment distribution show that negative electric dipole moments are locally formed on individual dimers on the surface. In addition, we obtained the dc bias voltage dependence of the εlocal(3) signal on a specific dimer by using an atom-tracking technique with NC-SNDM. We observed that the electric dipole induced a surface potential of around −250 mV on the dimer.
Tunable transport through a quantum dot chain with side-coupled Majorana bound states
Authors: Jiang Cui , Lu Gang , Gong Wei-Jiang
Published: September 2014

We investigate the transport properties of a quantum dot (QD) chain side-coupled to a pair of Majorana bound states (MBSs). It is found that the zero-bias conductance is tightly dependent on the parity of QD number. First, if a Majorana zero mode is introduced to couple to one QD of the odd-numbered QD structure, the zero-bias conductance is equal to e22h, but the zero-bias conductance will experience a valley-to-peak transition if the Majorana zero mode couples to the different QDs of the even-numbered QD structure. On the other hand, when the inter-MBS coupling is nonzero, the zero-bias conductance spectrum shows a peak in the odd-numbered QD structure, and in the even-numbered QD structure one conductance valley appears at the zero-bias limit. These results show the feasibility to manipulate the current in a multi-QD structure based on the QD-MBS coupling. Also, such a system can be a candidate for detecting the MBSs.
Tuning the ferroelectric state in multiferroic TbMnO3 single crystal by a trapped-charge-induced internal electric field
Authors: Zou Tao , Dun Zhiling , Cao Huibo , Zhu Mengze , Zhou Haidong , Ke Xianglin
Published: September 2014

The pyroelectric current effects in multiferroic TbMnO3 single crystal are reinvestigated in a wide temperature range. We report a pyroelectric current peak occurring around T = 107 K, which is much higher than the magnetic phase transition temperatures, after poling the sample from T ≥ 60 K to low temperatures, and we attribute it to the thermal release of trapped-charges in TbMnO3. We also show that the trapped-charges form a strong internal electric field that remarkably controls the ferroelectric polarization state induced by the cycloidal Mn3+ spins at lower temperature.
Theoretical simulations of protective thin film Fabry-Pérot filters for integrated optical elements of diode pumped alkali lasers (DPAL)
Authors: Quarrie L.
Published: September 2014

The lifetime of Diode-Pumped Alkali Lasers (DPALs) is limited by damage initiated by reaction of the glass envelope of its gain medium with rubidium vapor. Rubidium is absorbed into the glass and the rubidium cations diffuse through the glass structure, breaking bridging Si-O bonds. A damage-resistant thin film was developed enhancing high-optical transmission at natural rubidium resonance input and output laser beam wavelengths of 780 nm and 795 nm, while protecting the optical windows of the gain cell in a DPAL. The methodology developed here can be readily modified for simulation of expected transmission performance at input pump and output laser wavelengths using different combination of thin film materials in a DPAL. High coupling efficiency of the light through the gas cell was accomplished by matching the air-glass and glass-gas interfaces at the appropriate wavelengths using a dielectric stack of high and low index of refraction materials selected to work at the laser energies and protected from the alkali metal vapor in the gain cell. Thin films as oxides of aluminum, zirconium, tantalum, and silicon were selected allowing the creation of Fabry-Perot optical filters on the optical windows achieving close to 100% laser transmission in a solid optic combination of window and highly reflective mirror. This approach allows for the development of a new whole solid optic laser.
Carrier transport properties of the Group-IV ferromagnetic semiconductor Ge1-xFex with and without boron doping
Authors: Ban Yoshisuke , Wakabayashi Yuki , Akiyama Ryota , Nakane Ryosho , Tanaka Masaaki
Published: September 2014

We have investigated the transport and magnetic properties of group-IV ferromagnetic semiconductor Ge1-xFex films (x = 1.0 and 2.3%) with and without boron doping grown by molecular beam epitaxy (MBE). In order to accurately measure the transport properties of 100-nm-thick Ge1-xFex films, (001)-oriented silicon-on-insulator (SOI) wafers with an ultra-thin Si body layer (∼5 nm) were used as substrates. Owing to the low Fe content, the hole concentration and mobility in the Ge1-xFex films were exactly estimated by Hall measurements because the anomalous Hall effect in these films was found to be negligibly small. By boron doping, we increased the hole concentration in Ge1-xFex from ∼1018 cm−3 to ∼1020 cm−3 (x = 1.0%) and to ∼1019 cm−3 (x = 2.3%), but no correlation was observed between the hole concentration and magnetic properties. This result presents a contrast to the hole-induced ferromagnetism in III-V ferromagnetic semiconductors.
Size-dependent structure and magnetic properties of DyMnO3 nanoparticles
Authors: Cai Xuan , Shi Lei , Zhou Shiming , Zhao Jiyin , Guo Yuqiao , Wang Cailin
Published: September 2014

The structure and magnetic properties of orthorhombic DyMnO3 nanoparticles with different particle sizes are investigated in this paper. With decreasing particle size, all the lattice parameters a, b, and c gradually decrease, whereas the orthorhombic distortion increases. Magnetic measurements reveal that the antiferromagnetic interaction of Mn ions is weakened due to the decrease in Mn-O-Mn bond angle. Above a critical field H*, DyMnO3 undergoes a field-induced metamagnetic transition at 4 K, which is related to the spin reversal of Dy moments. The critical field H* increases monotonically with size reduction, indicating an enhancement of the antiferromagnetic interaction of Dy ions due to the decreased distance between rare earth ions. The magnetization at 4 K and 5 T, i.e., M(4 K, 5 T) shows a non-monotonic variation with particle size d, i.e., M(4 K, 5 T) initially increases with size reduction but decreases again for d < 68 nm. A modified core-shell model, in which the ferromagnetic ordering (Dy magnetic structure) and antiferromagnetic ordering (Mn magnetic structure) coexist in the core, is proposed to explain this behavior.
Structure and dynamics of cadmium telluride studied by x-ray and inelastic neutron scattering
Authors: Niedziela J. L. , Stone M. B.
Published: September 2014

We present a combined study of density functional theory, x-ray diffraction, and inelastic neutron scattering examining the temperature dependent structure and lattice dynamics of commercially available cadmium telluride. A subtle change in the structure is evinced near 80 K, which manifests also in the measured phonon density of states. There is no change to the long-range ordered structure. The implications of the change in relation to structural defects are discussed.
Phonon thermal conductivity of monolayer MoS2: A comparison with single layer graphene
Authors: Wei Xiaolin , Wang Yongchun , Shen Yulu , Xie Guofeng , Xiao Huaping , Zhong Jianxin , Zhang Gang
Published: September 2014

We investigate the size and edge roughness dependence on thermal conductivity of monolayer MoS2 (MLMoS2) by phonon Boltzmann transport equation combined with relaxation time approximation. The relative contribution of spectral phonons to thermal conductivity is explored, and we compared the characteristics of phonon transport with those in single layer graphene (SLG), which is a representative two-dimensional material. Quite different from SLG, because of the ultra-short intrinsic phonon mean free path, the thermal conductivity of MLMoS2 ribbons is size and roughness insensitive. The LA phonons have the major contribution to thermal conductivity of MLMoS2, and the ZA phonons in MLMoS2 have high relative contribution to thermal conductivity. The relative contribution to thermal conductivity from both high frequency and low frequency phonons in MLMoS2 is lower than that in SLG. The underlying mechanism of these distinct characteristics results from the different phonon dispersions and anharmonic characteristic between MLMoS2 and SLG.
Alleviating polarity-conflict at the heterointerfaces of KTaO3/GdScO3 polar complex-oxides
Authors: Thompson J. , Hwang J. , Nichols J. , Connell J. G. , Stemmer S. , Seo S. S. A.
Published: September 2014

We have synthesized and investigated the heterointerfaces of KTaO3 (KTO) and GdScO3 (GSO), which are both polar complex-oxides along the pseudo-cubic [001] direction. Since their layers have the same, conflicting net charges at interfaces, i.e., KO(−1)/ScO2(−1) or TaO2(+1)/GdO(+1), forming the heterointerface of KTO/GSO should be forbidden due to strong Coulomb repulsion, the so-called polarity conflict. However, we have discovered that atomic reconstruction occurs at the heterointerfaces between KTO thin-films and GSO substrates, which effectively alleviates the polarity conflict without destroying the hetero-epitaxy. Our result demonstrates one of the important ways to create artificial heterostructures from polar complex-oxides.
Formation of a buried silver nanowire network in borosilicate glass by solid-state ion exchange assisted by forward and reverse electric fields
Authors: Matsusaka Souta , Maehara Naotomo , Hidai Hirofumi , Chiba Akira , Morita Noboru , Itoi Takaomi
Published: September 2014

Using electric-field-assisted solid-state ion exchange, we formed a buried silver nanowire network in borosilicate glass. This procedure had two stages: a silver doping stage by applying voltage with silver as the anode (referred to as forward) and a silver precipitation stage by applying voltage in the opposite direction (referred to as reverse). Microscopic observations revealed many needle-like precipitates (100–300 nm in diameter) linked to each other, forming a thin layer at the bottom of the silver-doped area. The configuration of the layer formed in the glass matrix was precisely transferred from that of the dopant, silver foil in the present study. The embedded electrical wiring in the glass slide was tested using a patterned circuit-like silver foil as a dopant. Measuring the electrical resistance between two ends of the formed wire, we found that the embedded layer had high conductivity and acted as an electrical circuit.
Chemical reaction at ferromagnet/oxide interface and its influence on anomalous Hall effect
Authors: Liu Yi-Wei , Teng Jiao , Zhang Jing-Yan , Liu Yang , Wu Zheng-Long , Chen Xi , Li Xu-Jing , Feng Chun , Wang Hai-Cheng , Li Ming-Hua , Yu Guang-Hua
Published: September 2014

Chemical reactions at the ferromagnet/oxide interface in [Pt/Fe]3/MgO and [Pt/Fe]3/SiO2 multilayers before and after annealing were investigated by X-ray photoelectron spectroscopy. The results show that Fe atoms at the Fe/MgO interface were completely oxidized in the as-grown state and significantly deoxidized after vacuum annealing. However, only some of the Fe atoms at the Fe/SiO2 interface were oxidized and rarely deoxidized after annealing. The anomalous Hall effect was modified by this interfacial chemical reaction. The saturation anomalous Hall resistance (Rxy) was greatly increased in the [Pt/Fe]3/MgO multilayers after annealing and was 350% higher than that in the as-deposited film, while Rxy of the [Pt/Fe]3/SiO2 multilayer only increased 10% after annealing.
Salt stress differently affects growth, water status and antioxidant enzyme activities in Solanum lycopersicum and its wild relative Solanum chilense
Authors: Martínez Juan Pablo , Antúnez Alejandro , Araya Héctor , Pertuzé Ricardo , Fuentes Lida , Lizana X. Carolina , Lutts Stanley
Published: September 2014

The effect of saline stress (NaCl, 40, 80 and 160 mmol L−1 of NaCl) on growth, plant water status and leaf antioxidant enzyme activities was investigated in a commercial cultivar of cherry tomato (Solanum lycopersicum var. cerasiforme L.) and in a wild-related species collected in a salt-affected area of North Chile (Solanum chilense Dun.). Salt stress was applied in a nutrient solution at the vegetative stage during 40 days. The highest NaCl concentration reduced shoot relative growth, fresh and dry weight and leaf area in the cultivated S. lycopersicum but had less impact on S. chilense. Both species were able to efficiently perform osmotic adjustment but S. chilense also exhibited an increase in leaf succulence. The oxidative stress estimated through malondialdehyde quantification was always higher in the cultivated S. lycopersicum, both in the absence and in the presence of salt. Total superoxide dismutase activity (EC 1.15.1.1) increased in response to the highest dose of NaCl in S. chilense but remained constant in S. lycopersicum. Salinity induced an increase in ascorbate peroxidase (EC 1.11.1.11) in S. chilense but reduced it in S. lycopersicum. It is concluded that S. chilense displays efficient strategies to cope with high NaCl doses and that management of the oxidative status is a key mechanism allowing this species to tolerate salinity.