bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoelectrocatalytic microfluidic reactors utilizing hierarchical TiO2 nanotubes for determination of chemical oxygen demand
Authors: Heng Weixin , Zhang Wei , Zhang Qinghong , Wang Hongzhi , Li Yaogang
Published: May 2016

A novel and highly sensitive microfluidic device which integrated hierarchical TiO2 nanotubes exhibited an improved detection efficiency for determination of COD.
Suppression of lithium dendrite growth by introducing a low reduction potential complex cation in the electrolyte
Authors: Wu Borong , Liu Qi , Mu Daobin , Xu Hongliang , Wang Lei , Shi Lili , Gai Liang , Wu Feng
Published: May 2016

A low reduction potential complex cation (LRPCC) N-methyl-N-butylpiperidinium was introduced to the LiPF6/EC/DEC electrolyte to investigate its effect on the interface properties of a lithium anode.
Closing the gap between beliefs and practice: Change of pre-service chemistry teachers' orientations during a PCK-based NOS course
Authors: Demirdöğen Betül , Uzuntiryaki-Kondakçı Esen
Published: May 2016

The purpose of this case study was to investigate how pre-service chemistry teachers' science teaching orientations change during a two-semester intervention designed to enhance their pedagogical content knowledge (PCK) for teaching the nature of science (NOS). Moreover, the way that pre-service chemistry teachers translated their change in orientation into both their instructional planning and their PCK was examined. Thirty pre-service chemistry teachers enrolled in a Research in Science Education course participated in the study. Responses to an open-ended instrument, interviews, observations, and documents such as lesson plans and reflection papers were used as qualitative data sources. Through in-depth analysis of explicit PCK and further deductive analysis, we identified the influence of the intervention on participants' orientation and how participants translated their orientation into their planning and PCK. Analysis of data revealed that most of the pre-service teachers' naïve and transitional views about NOS changed into informed ideas after explicit-reflective NOS instruction. Participants revised their science teaching orientations by including more reform-based orientations at the end of the course (i.e., teaching NOS-related orientations). Their plans included at least one NOS aspect as an objective, which indicates that all of the participants designed their lesson plans with more informed views about at least one NOS aspect. In terms of aligning their reform-based orientations with other PCK components, pre-service chemistry teachers were more able to align their orientation with knowledge of instructional strategy and assessment than with knowledge of the learner. Implications for science teacher education and research are discussed.
Magnetic cylindrical colloids at liquid interfaces exhibit non-volatile switching of their orientation in an external field
Authors: Newton Bethany J. , Buzza D. Martin A.
Published: May 2016

Computer simulations of magnetic cylinders at liquid interfaces reveal unexpected orientational behaviour.
Exploring the dynamics of phase separation in colloid–polymer mixtures with long range attraction
Authors: Sabin Juan , Bailey Arthur E. , Frisken Barbara J.
Published: May 2016

Dynamic scaling and growth of structure in colloid–polymer samples spanning the phase diagram depend primarily on the strength of attraction.
Formation of uniform nitrogen-doped C/Ni/TiO2hollow spindles toward long cycle life lithium-ion batteries
Authors: Liu Yu , Gao Xuehui , Hong Zhanglian , Shi Weidong
Published: May 2016

Nitrogen-doped C/Ni/TiO2hollow spindles have been successfully constructed for long cycle life lithium-ion batteries.
Manganese dioxide nanosheet functionalized sulfur@PEDOT core–shell nanospheres for advanced lithium–sulfur batteries
Authors: Yan Min , Zhang Yang , Li Yu , Huo Yongqi , Yu Yong , Wang Chao , Jin Jun , Chen Lihua , Hasan Tawfique , Wang Binjie , Su Bao-Lian
Published: May 2016

MnO2nanosheet functionalized S@PEDOT core–shell nanospheres demonstrate highly enhanced electrochemical performance for Li–S batteries, benefitting from effectively trapping polysulfides, minimizing polysulfide dissolution, and improving cathode conductivity and wettability.
Construction of polydopamine-coated gold nanostars for CT imaging and enhanced photothermal therapy of tumors: an innovative theranostic strategy
Authors: Li Du , Zhang Yongxing , Wen Shihui , Song Yang , Tang Yueqin , Zhu Xiaoyue , Shen Mingwu , Mignani Serge , Majoral Jean-Pierre , Zhao Qinghua , Shi Xiangyang
Published: May 2016

A theranostic nanoplatform for in vivo CT imaging and enhanced PTT of tumors is reported.
Loading and release of fluorescent oligoarginine peptides into/from pH-responsive anionic supramolecular nanoparticles
Authors: Graña-Suárez Laura , Verboom Willem , Buckle Tessa , Rood Mark , van Leeuwen Fijs W. B. , Huskens Jurriaan
Published: May 2016

The uptake and release of fluorescent oligoarginines was studied into/from a pH-sensitive system based on negatively charged fluorescent supramolecular nanoparticles.
Isomeric indacenedibenzothiophenes: synthesis, photoelectric properties and ambipolar semiconductivity
Authors: Ren Longbin , Liu Chunming , Wang Zhaohui , Zhu Xiaozhang
Published: May 2016

Isomeric indacenedibenzothiophenes featuring unique photoelectric properties were synthesized using a new strategy via double C–H activation cyclization. Single-crystal field-effect transistors based on IDBT-l-TIPSA delivered high and balanced ambipolar property under ambient conditions.
Asymmetrical 1:2 Y‐tree interconnects modelling with Kron–Branin formalism
Authors: Ravelo B. , Maurice O. , Lalléchère S.
Published: May 2016

This research work presents an innovative tensorial analysis of network (TAN) model of asymmetrical 1:2 Y‐tree interconnects. The modelling methodology is built with Kron–Branin formalism. The analytical Z‐matrix equivalent to the assumed multi‐port system is fundamentally established from the transmission line Kron–Branin topology. Then, the equivalent S‐parameters of the two‐level Y‐tree system are established. The developed model is validated with S‐parameter simulations of microstrip Y‐tree interconnects structure from DC to 8 GHz.
Colour FAST (CFAST) match: fast affine template matching for colour images
Authors: Jia Di , Cao Jun , Song Wei‐dong , Tang Xiao‐liang , Zhu Hong
Published: May 2016

Fast‐match is a fast and effective algorithm for template matching. However, when matching colour images, the images are converted into greyscale images. The colour information is lost in this process, resulting in errors in areas with distinctive colours but similar greyscale values An improved fast‐match algorithm that utilises all three RGB channels to construct colour sum‐of‐absolute‐differences (CSAD) is proposed, thus improving the sum‐of‐absolute‐differences distance used in fast‐match. In this algorithm, each pixel in the image is categorised by clustering them using density‐based spatial clustering of applications with noise (DBSCAN) algorithm over the RGB vector, then the number of pixels in each category and the cumulative RGB values for each RGB channel are calculated to identify the centroid of each category. The RGB vector centroid is used as the CSAD decision criteria, and inverse of number of pixels in each category is used as the differentiating coefficient to construct a new similarity measure. Experiment results demonstrate that this algorithm has significant higher accuracy for matching colour images than the original fast‐match algorithm.
Carrier aggregation‐based dynamic spectrum access framework for LTE‐A primary operators
Authors: AbdelFadeel Khaled Qorany , Khattab Ahmed , Elsayed Khaled , Digham Fadel
Published: May 2016

In this study, the authors tackle the dynamic spectrum access (DSA) problem for primary operators (POs) for long‐term evolution‐advanced (LTE‐A) systems. They propose an auction‐based DSA framework that exploits the capabilities of carrier aggregation to efficiently utilise the under‐utilised spectrum which varies with time and space. Their proposed dynamic access framework defines the LTE‐A resource allocation problem as a bounded knapsack auction (BKA). They solve such a BKA by converting it to a 0–1 knapsack problem that is solved using dynamic programming. Unlike prior work, they are the first to introduce an accurate model for estimating the bandwidth required to satisfy the traffic demands of an LTE‐A operator’s subscribers for a projected demand model. Using extensive simulations of such a realistic network model, the results of their framework show more than 20% reduction in the required spectrum and up to 80% reduction in the average under‐utilised spectrum compared with traditional static spectrum access widely adopted by spectrum regulation authorities. The reduction in the average under‐utilised spectrum becomes 93.3% with 250% higher revenue compared with existing dynamic allocation strategies that are directly formulated as 0–1 knapsack auctions.
Massive MIMO: survey and future research topics
Authors: Araújo Daniel C. , Maksymyuk Taras , de Almeida André L.F. , Maciel Tarcisio , Mota João C.M. , Jo Minho
Published: May 2016

Massive multiple‐input multiple‐output technology has been considered a breakthrough in wireless communication systems. It consists of equipping a base station with a large number of antennas to serve many active users in the same time–frequency block. Among its underlying advantages is the possibility to focus transmitted signal energy into very short‐range areas, which will provide huge improvements in terms of system capacity. However, while this new concept renders many interesting benefits, it brings up new challenges that have called the attention of both industry and academia: channel state information acquisition, channel feedback, instantaneous reciprocity, statistical reciprocity, architectures, and hardware impairments, just to mention a few. This paper presents an overview of the basic concepts of massive multiple‐input multiple‐output, with a focus on the challenges and opportunities, based on contemporary research.
Soliton mode‐locked erbium‐doped fibre laser with mechanically exfoliated molybdenum disulphide saturable absorber
Authors: Ahmed Mahmoud Hazzaa M. , Latiff Anas A. , Arof Hamzah , Ahmad Harith , Harun Sulaiman Wadi
Published: May 2016

The authors demonstrate the generation of soliton mode‐locked pulses from an erbium‐doped fibre ring laser incorporating molybdenum disulphide (MoS2) saturable absorber (SA) with a net anomalous dispersion. The MoS2 SA is prepared by mechanically exfoliating MoS2 crystal and fixing the acquired MoS2 flakes onto the end surface of a standard FC/PC fibre connector. A self‐started mode‐locked soliton pulse is generated by fine‐tuning the rotation of the polarisation controller at the threshold pump power of 50 mW. Its solitonic behaviour is verified by the presence of Kelly sidebands in the output spectrum. The central wavelength, 3 dB bandwidth, pulsewidth, and repetition rate of the laser are 1598.94 nm, 5.4 nm, 0.83 ps, and 17.1 MHz, respectively. The maximum pulse energy is 74 nJ at pump power of 110 mW with the output power of 1.26 mW. The MoS2 SA was constructed in a simple fabrication process and has a modulation depth of 11.3% to successfully produce the stable soliton mode‐locked fibre laser.
Fabrication of two‐dimensional photonic quasi‐crystals with 18‐ and 36‐fold by holography for solar application
Authors: Varadarajan Vadivelan , Shekar Chandar
Published: May 2016

Holographic lithography has been widely used to the realisation of complex photonic structures such as photonic crystal and quasi‐photonic crystals. Dual‐beam multi‐exposure holographic technique was adopted for the fabrication of 18‐fold and 36‐fold sub‐microscopic rotational symmetric structures; the fabricated photonic quasi‐crystals examined by laser diffraction pattern, optical and scanning electron microscopes. Here, the authors have fabricated photonic quasi‐crystals in photoresist and the structure was transformed into metal, the transferred structure in metal could act as a substrate/or back reflector for the thin film solar cell. Further work on concentration of solar light by photonic quasi‐crystals is progressing.
Structural health monitoring of composite wind turbine blades: challenges, issues and potential solutions
Authors: Yang Wenxian , Peng Zhike , Wei Kexiang , Tian Wenye
Published: May 2016

Wind turbine (WT) blades are vulnerable to failure as they are exposed to direct harsh environment, suffering constantly varying loads by wind and cyclic fatigue load due to self‐weight, experiencing extreme temperature and humidity changes, erosion and corrosion. As a consequence, blades show high failure rate and share significant downtime, which highlight the significance and essentiality of the research, development and application of blade structural health monitoring (SHM) techniques. To fulfil reliable SHM of WT blades, much effort has been spent in the past years as reported in the literature. However, to date, how to realise reliable WT blade SHM is still an open question. The previous reviews enumerate the non‐destructive testing techniques that are potentially applicable to blade SHM, but they fail to indicate which technique is most suitable for blade SHM and how to implement reliable SHM of a WT blade. To fill this gap, this study is geared toward to investigate the pros and cons of existing blade SHM techniques and following which, a newly developed blade SHM technique that is effective in both damage detection and fault location is discussed.
Synthesis of carbon nanostructures from coal by chemical solid synthesis method
Authors: Vakili Fathabadi Motahare , Hashemipour Rafsanjani Hasan , Danafar Firouze
Published: May 2016

Carbon nanofibres (CNFs) and carbon spheres (CSs) are successfully synthesised using coal particles (<44 micron) in solid phase. Coal and ferrocene as catalyst were fed to the reactor in the solid form. The reaction is carried out in a tubular reactor. The as‐synthesised samples have been characterised through Raman spectroscopy, X‐ray diffraction, scanning and transmission electron microscopy. The results show CNFs formed in 25–40 nm and mono dispersed CSs in 200–300 nm are amorphous. A feasible mechanism of CNFs and CSs formation from coal described here with the help of coal structure.
Ultraviolet-photoelectric effect for augmented contrast and resolution in electron microscopy
Authors: Seniutinas Gediminas , Balčytis Armandas , Juodkazis Saulius
Published: May 2016

A new tool providing material contrast control in scanning electron microscopy (SEM) is demonstrated. The approach is based on deep-UV illumination during SEM imaging and delivers a novel material based contrast as well as higher resolution due to the photoelectric effect. Electrons liberated from illuminated sample surface contribute to the imaging which can be carried out at a faster acquisition rate, provide material selective contrast, reduce distortions caused by surface charging, and can substitute metal coating in SEM. These features provide high fidelity SEM imaging and are expected to significantly improve the performance of electron beam instruments as well as to open new opportunities for imaging and characterization of materials at the nanoscale.
A microchip laser source with stable intensity and frequency used for self-mixing interferometry
Authors: Zhang Shaohui , Zhang Shulian , Tan Yidong , Sun Liqun
Published: May 2016

We present a stable 40 × 40 × 30 mm3 Laser-diode (LD)-pumped-microchip laser (ML) laser source used for self-mixing interferometry which can measure non-cooperative targets. We simplify the coupling process of pump light in order to make its polarization and intensity robust against environmental disturbance. Thermal frequency stabilization technology is used to stabilize the laser frequency of both LD and ML. Frequency stability of about 1 × 10−7 and short-term intensity fluctuation of 0.1% are achieved. The theoretical long-term displacement accuracy limited by frequency and intensity fluctuation is about 10 nm when the measuring range is 0.1 m. The line-width of this laser is about 25 kHz corresponding to 12 km coherent length and 6 km measurement range for self-mixing interference. The laser source has been equipped to a self-mixing interferometer, and it works very well.
Perfect optical vortex enhanced surface plasmon excitation for plasmonic structured illumination microscopy imaging
Authors: Zhang Chonglei , Min Changjun , Du Luping , Yuan X.-C.
Published: May 2016

We propose an all-optical technique for plasmonic structured illumination microscopy (PSIM) with perfect optical vortex (POV). POV can improve the efficiency of the excitation of surface plasma and reduce the background noise of the excited fluorescence. The plasmonic standing wave patterns are excited by POV with fractional topological charges for accurate phase shift of {−2π/3, 0, and 2π/3}. The imaging resolution of less than 200 nm was produced. This PSIM technique is expected to be used as a wide field, super resolution imaging technique in dynamic biological imaging.
On the ultrafast photo-induced dynamics of α-terpinene
Authors: Gao Yan , Pemberton Christine C. , Zhang Yao , Weber Peter M.
Published: May 2016

The ultrafast relaxation pathway of α-terpinene was studied by photoionization-photoelectron spectroscopy for a range of excitation conditions. Time-resolved spectra were obtained upon optical excitation with ultrashort laser pulses at 5.56 eV, 4.96 eV, 4.76 eV, and 4.56 eV, followed by ionization with 3.06 eV pulses. The experiments yielded spectra of the initially excited state, which decays with a time constant of 66 fs, independent of the excitation wavelength. We also observed a sequential series of Rydberg peaks, including the s, p, and d states with n = 3–6, which capture the travel times on the ensuing reaction path. There is no statistically significant dependence of the travel time on the excitation energy. A comparison of the time-dependent signals with those of the un-substituted parent molecule, 1,3-cyclohexadiene, shows that the substituents on α-terpinene slow the reaction down by a factor of about 2.
The structure of water at a Pt(111) electrode and the potential of zero charge studied from first principles
Authors: Sakong Sung , Forster-Tonigold Katrin , Groß Axel
Published: May 2016

The structure of a liquid water layer on Pt(111) has been studied by ab initio molecular dynamics simulations based on periodic density functional theory calculations. First the reliability of the chosen exchange-correlation function has been validated by considering water clusters, bulk ice structures, and bulk liquid water, confirming that the dispersion corrected RPBE-D3/zero functional is a suitable choice. The simulations at room temperature yield that a water layer that is six layers thick is sufficient to yield liquid water properties in the interior of the water film. Performing a statistical average along the trajectory, a mean work function of 5.01 V is derived, giving a potential of zero charge of Pt(111) of 0.57 V vs. standard hydrogen electrode, in good agreement with experiments. Therefore we propose the RPBE-D3/zero functional as the appropriate choice for first-principles calculations addressing electrochemical aqueous electrolyte/metal electrode interfaces.
The DQ and DQΦ electronic structure diabatization methods: Validation for general applications
Authors: Hoyer Chad E. , Parker Kelsey , Gagliardi Laura , Truhlar Donald G.
Published: May 2016

We recently proposed the dipole-quadrupole (DQ) method for transforming adiabatic electronic states to diabatic states by using matrix elements of the dipole and quadrupole operators, and we applied the method to 3-state diabatizations of LiH and phenol. Here we extend the method to also include the electrostatic potential, and we call the resulting method the DQΦ method, which denotes the dipole–quadrupole–electrostatic-potential diabatization method. The electrostatic potential provides extra flexibility, and the goal of the present work is to test and illustrate the robustness of the methods for producing diabatic potential energy curves that tend to the adiabatic curves away from crossings and avoided crossings and are smooth in regions of crossings and avoided crossings. We illustrate the generality of the methods by an application to LiH with four states and by two-state diabatizations of HCl, (H2)2, O3, and the reaction Li + HF → LiF + H. We find that—if enough states are included—the DQ method does not have a significant dependence on the parameter weighting the quadrupole moment, and a geometry-independent value of 10 a0−2 is adequate in all cases tested. We also find that the addition of the electrostatic potential improves the diabatic potentials in some cases and provides an additional property useful for increasing the generality of the method for diabatization.
Mixing in lock-release gravity currents propagating up a slope
Authors: Ottolenghi L. , Adduce C. , Inghilesi R. , Roman F. , Armenio V.
Published: May 2016

Lock-exchange gravity currents propagating up a slope are investigated by large eddy simulations, focusing on the entrainment and mixing processes occurring between the dense current and the ambient fluid. Relevant parameters, such as the aspect ratio of the initial volume of dense fluid in the lock R, the angle between the bottom boundary and the horizontal direction θ and the depth aspect ratio ϕ, are varied. The numerical results are compared with laboratory experiments and a good agreement is found. Entrainment and mixing in a lock-release gravity current are studied using different entrainment parameters and an energy budget method. The entrainment is found to depend on both Froude, Fr, and Reynolds, Re, numbers. In addition, the dependence of both entrainment and mixing on the parameters varied is discussed. The entrainment decreases with increasing steepness of the bottom and R. Irreversible mixing is not affected by the varied parameters during the slumping phase, while during the successive phases of motion, it is found to decrease with the increase of θ and R. Low entrainment and mixing occur for ϕ < 1.
Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. I. Triples expansions
Authors: Eriksen Janus J. , Matthews Devin A. , Jørgensen Poul , Gauss Jürgen
Published: May 2016

The accuracy at which total energies of open-shell atoms and organic radicals may be calculated is assessed for selected coupled cluster perturbative triples expansions, all of which augment the coupled cluster singles and doubles (CCSD) energy by a non-iterative correction for the effect of triple excitations. Namely, the second- through sixth-order models of the recently proposed CCSD(T–n) triples series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)] are compared to the acclaimed CCSD(T) model for both unrestricted as well as restricted open-shell Hartree-Fock (UHF/ROHF) reference determinants. By comparing UHF- and ROHF-based statistical results for a test set of 18 modest-sized open-shell species with comparable RHF-based results, no behavioral differences are observed for the higher-order models of the CCSD(T–n) series in their correlated descriptions of closed- and open-shell species. In particular, we find that the convergence rate throughout the series towards the coupled cluster singles, doubles, and triples (CCSDT) solution is identical for the two cases. For the CCSD(T) model, on the other hand, not only its numerical consistency, but also its established, yet fortuitous cancellation of errors breaks down in the transition from closed- to open-shell systems. The higher-order CCSD(T–n) models (orders n > 3) thus offer a consistent and significant improvement in accuracy relative to CCSDT over the CCSD(T) model, equally for RHF, UHF, and ROHF reference determinants, albeit at an increased computational cost.
Alternative view of two-dimensional spectroscopy
Authors: Gelin Maxim F. , Domcke Wolfgang
Published: May 2016

Femtosecond two-dimensional (2D) spectroscopy has become a widely employed method for the investigation of the dynamics of complex chemical and biological systems. In 2D spectroscopy, the sample is excited with three phase-locked femtosecond pulses, and the signal is heterodyned with the local oscillator field. The 2D spectrum is obtained by double Fourier transform with respect to the time delay between the first two pulses and the time delay between the third pulse and the local oscillator field. We show that 2D optical signals can alternatively be measured and computationally simulated as four-wave-mixing signals generated by two femtosecond pulses and two one-sided continuous-wave (CW) pulses. The first femtosecond pulse and one-sided CW pulse create the doorway state, while the second femtosecond pulse and one-sided CW pulse create the window state. This picture relates 2D spectroscopy to other mixed time-frequency-domain techniques, which is useful for the interpretation of the corresponding signals. Moreover, it allows a computationally efficient evaluation of 2D spectra.
Comparative assessment of density functional methods for evaluating essential parameters to simulate SERS spectra within the excited state energy gradient approximation
Authors: Mohammadpour Mozhdeh , Jamshidi Zahra
Published: May 2016

The prospect of challenges in reproducing and interpretation of resonance Raman properties of molecules interacting with metal clusters has prompted the present research initiative. Resonance Raman spectra based on the time-dependent gradient approximation are examined in the framework of density functional theory using different methods for representing the exchange-correlation functional. In this work the performance of different XC functionals in the prediction of ground state properties, excitation state energies, and gradients are compared and discussed. Resonance Raman properties based on time-dependent gradient approximation for the strongly low-lying charge transfer states are calculated and compared for different methods. We draw the following conclusions: (1) for calculating the binding energy and ground state geometry, dispersion-corrected functionals give the best performance in comparison to ab initio calculations, (2) GGA and meta GGA functionals give good accuracy in calculating vibrational frequencies, (3) excited state energies determined by hybrid and range-separated hybrid functionals are in good agreement with EOM-CCSD calculations, and (4) in calculating resonance Raman properties GGA functionals give good and reasonable performance in comparison to the experiment; however, calculating the excited state gradient by using the hybrid functional on the hessian of GGA improves the results of the hybrid functional significantly. Finally, we conclude that the agreement of charge-transfer surface enhanced resonance Raman spectra with experiment is improved significantly by using the excited state gradient approximation.
An optimal power sharing and power control strategy of photovoltaic/fuel cell/ultra-capacitor hybrid power system
Authors: Kamal T. , Hassan S. Z. , Espinosa-Trujillo M. J. , Li H. , Flota M.
Published: May 2016

Renewable energy sources experience problems such as deregulation when they are used as stand-alone energy sources. This paper presents an optimal power sharing and power control strategy combining a photovoltaic (PV) array, a fuel cell (FC) stack, an ultra-capacitor (UC) module, and a set of loads. The photovoltaic is the prior energy source while the fuel cell (FC) system is added as a backup source to meet the excess power demand. The ultra-capacitor (UC) is utilized as a buffer storage to compensate the slow dynamic response of the FC during transient and regulate the DC-bus voltage. The power control strategy is designed to work on a two-level arrangement. The top level controls the entire power management, which generates references to low level individual subsystems depending upon solar radiation, temperature, and load conditions. Based on the command signals, each local controller controls the PV, FC, electrolyzer, and UC. The top level also controls the load scheduling during low solar radiation in order to sustain the system operation for 24 h. The performance of the system is tested under real-world record of solar radiation, temperature, and load conditions for Bahria town at Islamabad, Pakistan. The effectiveness of the proposed model in terms of voltage regulation, power transfer, load tracking, and grid stability is verified by Matlab simulation results.
Femtosecond broadband fluorescence upconversion spectroscopy: Spectral coverage versus efficiency
Authors: Gerecke Mario , Bierhance Genaro , Gutmann Michael , Ernsting Nikolaus P. , Rosspeintner Arnulf
Published: May 2016

Sum frequency mixing of fluorescence and ∼1300 nm gate pulses, in a thin β-barium borate crystal and non-collinear type II geometry, is quantified as part of a femtosecond fluorimeter [X.-X. Zhang et al., Rev. Sci. Instrum. 82, 063108 (2011)]. For a series of fixed phasematching angles, the upconversion efficiency is measured depending on fluorescence wavelength. Two useful orientations of the crystal are related by rotation around the surface normal. Orientation A has higher efficiency (factor ∼3) compared to B at the cost of some loss of spectral coverage for a given crystal angle. It should be used when subtle changes of an otherwise stationary emission band are to be monitored. With orientation B, the fluorescence range λF > 420-750 nm is covered with a single setting of the crystal and less gate scatter around time zero. The accuracy of determining an instantaneous emission band shape is demonstrated by comparing results from two laboratories.
Effect of doping on room temperature carrier escape mechanisms in InAs/GaAs quantum dot p-i-n junction photovoltaic cells
Authors: Sellers D. G. , Chen E. Y. , Polly S. J. , Hubbard S. M. , Doty M. F.
Published: May 2016

We investigate the effect of doping on the mechanisms of carrier escape from intermediate states in delta-doped InAs/GaAs intermediate band solar cells. The intermediate states arise from InAs quantum dots embedded in a GaAs p-i-n junction cell. We find that doping the sample increases the number of excited-state carriers participating in a cycle of trapping and carrier escape via thermal, optical, and tunneling mechanisms. However, we find that the efficiency of the optically-driven carrier escape mechanism is independent of doping and remains small.
The Weyl realizations of Lie algebras, and left–right duality
Authors: Meljanac Stjepan , Krešić–Jurić Saša , Martinić Tea
Published: May 2016

We investigate dual realizations of non-commutative spaces of Lie algebra type in terms of formal power series in the Weyl algebra. To each realization of a Lie algebra 𝔤 we associate a star-product on the symmetric algebra S(𝔤) and an ordering on the enveloping algebra U(𝔤). Dual realizations of 𝔤 are defined in terms of left–right duality of the star-products on S(𝔤). It is shown that the dual realizations are related to an extension problem for 𝔤 by shift operators whose action on U(𝔤) describes left and right shift of the generators of U(𝔤) in a given monomial. Using properties of the extended algebra, in the Weyl symmetric ordering we derive closed form expressions for the dual realizations of 𝔤 in terms of two generating functions for the Bernoulli numbers. The theory is illustrated by considering the κ-deformed space.
High density nitrogen-vacancy sensing surface created via He+ ion implantation of 12C diamond
Authors: Kleinsasser Ed E. , Stanfield Matthew M. , Banks Jannel K. Q. , Zhu Zhouyang , Li Wen-Di , Acosta Victor M. , Watanabe Hideyuki , Itoh Kohei M. , Fu Kai-Mei C.
Published: May 2016

We present a promising method for creating high-density ensembles of nitrogen-vacancy centers with narrow spin-resonances for high-sensitivity magnetic imaging. Practically, narrow spin-resonance linewidths substantially reduce the optical and RF power requirements for ensemble-based sensing. The method combines isotope purified diamond growth, in situ nitrogen doping, and helium ion implantation to realize a 100 nm-thick sensing surface. The obtained 1017 cm−3 nitrogen-vacancy density is only a factor of 10 less than the highest densities reported to date, with an observed 200 kHz spin resonance linewidth over 10 times narrower.
Effect of asymmetric concentration profile on thermal conductivity in Ge/SiGe superlattices
Authors: Hahn Konstanze R. , Cecchi Stefano , Colombo Luciano
Published: May 2016

The effect of the chemical composition in Si/Ge-based superlattices on their thermal conductivity has been investigated using molecular dynamics simulations. Simulation cells of Ge/SiGe superlattices have been generated with different concentration profiles such that the Si concentration follows a step-like, a tooth-saw, a Gaussian, and a gamma-type function in direction of the heat flux. The step-like and tooth-saw profiles mimic ideally sharp interfaces, whereas Gaussian and gamma-type profiles are smooth functions imitating atomic diffusion at the interface as obtained experimentally. Symmetry effects have been investigated comparing the symmetric profiles of the step-like and the Gaussian function to the asymmetric profiles of the tooth-saw and the gamma-type function. At longer sample length and similar degree of interdiffusion, the thermal conductivity is found to be lower in asymmetric profiles. Furthermore, it is found that with smooth concentration profiles where atomic diffusion at the interface takes place the thermal conductivity is higher compared to systems with atomically sharp concentration profiles.
The effect of embedded nanopillars on the built-in electric field of amorphous silicon p-i-n devices
Authors: Kirkpatrick T. , Simmons C. B. , Akey A. J. , Tabet N. , Buonassisi T.
Published: May 2016

In this work, we report on the experimental modification of the built-in electric field of a-Si:H p-i-n junctions, resulting from Ag nanopillars embedded within the intrinsic layer (i-layer). Increased open-circuit voltages, from J-V traces, and reduced charge transit-times, from time-of-flight (ToF) measurements, indicate that the built-in electric field within the i-layer is increased with respect to unstructured reference samples. Decreased short-circuit current density values coupled with competing diode J-V characteristics, however, indicate that the charge collection from the i-layer is significantly decreased for the nanopillar samples. Theoretical and functional analysis of the ToF data reaffirms both reduced charge-transit times and decreased charge collection, and is able to quantitatively confirm the enhanced built-in electric field of the nanopillar samples.
Internal resonance with commensurability induced by an auxiliary oscillator for broadband energy harvesting
Authors: Xiong Liuyang , Tang Lihua , Mace Brian R.
Published: May 2016

An internal resonance based broadband vibration energy harvester is proposed by introducing an auxiliary oscillator to the main nonlinear harvesting oscillator. Compared to conventional nonlinear energy harvesters, the natural frequencies of this two-degree-of-freedom nonlinear system can be easily adjusted to be commensurable which will result in more resonant peaks and better wideband performance. Experimental measurements and equivalent circuit simulations demonstrate that this design outperforms its linear counterpart. In addition to the open-circuit voltage, the optimal resistance to obtain the maximum power is determined. Nearly 130% increase in the bandwidth is achieved compared to the linear counterpart at an excitation level of 2 m/s2. The findings provide insight for the design of a broadband energy harvester when there is nonlinearity and internal resonance.
Cerenkov emission of acoustic phonons electrically generated from three-dimensional Dirac semimetals
Authors: Kubakaddi S. S.
Published: May 2016

Cerenkov acoustic phonon emission is theoretically investigated in a three-dimensional Dirac semimetal (3DDS) when it is driven by a dc electric field E. Numerical calculations are made for Cd3As2 in which mobility and electron concentration are large. We find that Cerenkov emission of acoustic phonons takes place when the electron drift velocity vd is greater than the sound velocity vs. This occurs at small E (∼few V/cm) due to large mobility. Frequency (ωq) and angular (θ) distribution of phonon emission spectrum P(ωq, θ) are studied for different electron drift velocities vd (i.e., different E) and electron concentrations ne. The frequency dependence of P(ωq, θ) shows a maximum Pm(ωq, θ) at about ωm ≈ 1 THz and is found to increase with the increasing vd and ne. The value of ωm shifts to higher region for larger ne. It is found that ωm/ne1/3 and Pm(ωq, θ)/ne2/3 are nearly constants. The latter is in contrast with the Pm(ωq, θ)ne1/2 = constant in conventional bulk semiconductor. Each maximum is followed by a vanishing spectrum at nearly “2kf cutoff,” where kf is the Fermi wave vector. Angular dependence of P(ωq, θ) and the intensity P(θ) of the phonon emission shows a maximum at an emission angle 45° and is found to increase with increasing vd. P(θ) is found to increase linearly with ne giving the ratio P(θ)/(nevd) nearly a constant. We suggest that it is possible to have the controlled Cerenkov emission and generation of acoustic phonons with the proper choice of E, θ, and ne. 3DDS with large ne and mobility can be a good source of acoustic phonon generation in ∼THz regime.
Long-lived pressure-driven coherent structures in KSTAR plasmas
Authors: Lee S. G. , Seol J. , Lee H. H. , Aydemir A. Y. , Terzolo L. , Lee K. D. , Bae Y. S. , Bak J. G. , Choe G. H. , Yun G. S. , Yoo J. W.
Published: May 2016

Highly coherent structures associated with an extremely long-lived saturated magnetohydrodynamic instability have been observed in KSTAR tokamak under a long-pulse and steady-state operation. They persist essentially unchanged for the full duration of a discharge up to 40 s, much longer than any dynamical or dissipative time scales in the system. Analysis of the data, supported by numerical simulations, indicates that they may be associated with a pressure-driven mode causing some degradation in the toroidal rotation, electron, and ion energy confinement.
High-frequency operation of a mid-infrared interband cascade system at room temperature
Authors: Lotfi Hossein , Li Lu , Lei Lin , Ye Hao , Shazzad Rassel S. M. , Jiang Yuchao , Yang Rui Q. , Mishima Tetsuya D. , Santos Michael B. , Gupta James A. , Johnson Matthew B.
Published: May 2016

The high-frequency operation of a mid-infrared interband cascade system that consists of a type-I interband cascade laser and an uncooled interband cascade infrared photodetector (ICIP) is demonstrated at room temperature. The 3-dB bandwidth of this system under direct frequency modulation was ∼850 MHz. A circuit model was developed to analyze the high-frequency characteristics. The extracted 3-dB bandwidth for an uncooled ICIP was ∼1.3 GHz, signifying the great potential of interband cascade structures for high-speed applications. The normalized Johnson-noise-limited detectivity of these ICIPs exceeded 109 cm Hz1/2/W at 300 K. These results validate the advantage of ICIPs to achieve both high speed and high sensitivity at high temperatures.
Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil
Authors: Calabrese Gabriele , Corfdir Pierre , Gao Guanhui , Pfüller Carsten , Trampert Achim , Brandt Oliver , Geelhaar Lutz , Fernández-Garrido Sergio
Published: May 2016

We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit an equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.
Influence of the “second gap” on the transparency of transparent conducting oxides: An ab initio study
Authors: Ha Viet-Anh , Waroquiers David , Rignanese Gian-Marco , Hautier Geoffroy
Published: May 2016

Transparent conducting oxides (TCOs) are essential to many technologies. These materials are doped (n- or p-type) oxides with a large enough band gap (ideally >3 eV) to ensure transparency. However, the high carrier concentration present in TCOs leads additionally to the possibility for optical transitions from the occupied conduction bands to higher states for n-type materials and from lower states to the unoccupied valence bands for p-type TCOs. The “second gap” formed by these transitions might limit transparency, and a large second gap has been sometimes proposed as a design criteria for high performance TCOs. Here, we study the influence of this second gap on optical absorption using ab initio computations for several well-known n- and p-type TCOs. Our work demonstrates that most known n-type TCOs do not suffer from second gap absorption in the visible even at very high carrier concentrations. On the contrary, p-type oxides show lowering of their optical transmission for high carrier concentrations due to second gap effects. We link this dissimilarity to the different chemistries involved in n- versus typical p-type TCOs. Quantitatively, we show that second gap effects lead to only moderate loss of transmission (even in p-type TCOs) and suggest that a wide second gap, while beneficial, should not be considered as a needed criteria for a working TCO.
Neutron depolarization imaging of the hydrostatic pressure dependence of inhomogeneous ferromagnets
Authors: Schulz M. , Neubauer A. , Böni P. , Pfleiderer C.
Published: May 2016

The investigation of fragile and potentially inhomogeneous forms of ferromagnetic order under extreme conditions, such as low temperatures and high pressures, is of central interest for areas such as geophysics, correlated electron systems, as well as the optimization of materials synthesis for applications where particular material properties are required. We report neutron depolarization imaging measurements on the weak ferromagnet Ni3Al under pressures up to 10 kbar using a Cu:Be clamp cell. Using a polychromatic neutron beam with wavelengths λ≥4 Å in combination with 3He neutron spin filter cells as polarizer and analyzer, we were able to track differences of the pressure response in inhomogeneous samples by virtue of high resolution neutron depolarization imaging. This provides spatially resolved and non-destructive access to the pressure dependence of the magnetic properties of inhomogeneous ferromagnetic materials.
Ionic liquid gating on atomic layer deposition passivated GaN: Ultra-high electron density induced high drain current and low contact resistance
Authors: Zhou Hong , Du Yuchen , Ye Peide D.
Published: May 2016

Herein, we report on achieving ultra-high electron density (exceeding 1014 cm−2) in a GaN bulk material device by ionic liquid gating, through the application of atomic layer deposition (ALD) of Al2O3 to passivate the GaN surface. Output characteristics demonstrate a maximum drain current of 1.47 A/mm, the highest reported among all bulk GaN field-effect transistors, with an on/off ratio of 105 at room temperature. An ultra-high electron density exceeding 1014 cm−2 accumulated at the surface is confirmed via Hall-effect measurement and transfer length measurement. In addition to the ultra-high electron density, we also observe a reduction of the contact resistance due to the narrowing of the Schottky barrier width on the contacts. Taking advantage of the ALD surface passivation and ionic liquid gating technique, this work provides a route to study the field-effect and carrier transport properties of conventional semiconductors in unprecedented ultra-high charge density regions.
Large enhancement of the electrocaloric effect in PLZT ceramics prepared by hot-pressing
Authors: Zhang Guangzu , Chen Zhibiao , Fan Baoyan , Liu Jianguo , Chen Mo , Shen Meng , Liu Pin , Zeng Yike , Jiang Shenglin , Wang Qing
Published: May 2016

In this contribution, we demonstrate the optimization of the microstructures of the Pb0.85La0.1(Zr0.65Ti0.35)O3 (PLZT) relaxor ferroelectric ceramics and subsequent enhancements in their polarization and electrical resistivity by using a hot-pressing process. The resulting superior breakdown strength of hot-pressed PLZT enables the application of high electric field to induce a giant electrocaloric effect, in which the adiabatic change of temperature (ΔT) and the isothermal change of entropy (ΔS) are around 2 times greater than those of the samples prepared by the conventional sintering approach using muffle furnace. Moreover, the addition of extra PbO to make up the loss of Pb in the high-temperature sintering leads to the further improvements in the phase composition and electrical properties of PLZT, due to inhibition of the pyrochlore phase formation. The relationship among the sintering conditions, the content of excess PbO, and the microstructure as well as the electrical characteristics of PLZT have been investigated in a systematic manner. This work provides a facile approach to enhanced electrocaloric effect in bulk ceramics.
Distance protection optimization strategy for distribution systems with battery energy storage system
Authors: Yang Lian , Tai Nengling , Fan Chunju , Huang Wentao
Published: May 2016

Battery Energy Storage System (BESS) is a type of clean energy, which is able to enhance energy efficiency. However, the connection of the BESS with distribution systems has an impact on the conventional protection. This paper presents the BESS operation characteristics and its impact on distance protection. Optimal strategy of Zone II is analyzed from the perspective of impedance originally. The BESS has three operation statuses which will be studied separately. When a fault occurs at different locations of feeders downstream, the fault current of the BESS increases nonlinearly. By defining two original concepts, critical impedance and maximum protection impedance, the nonlinear output current is classified into two parts. Protect access capacity and protection sensitivity are analyzed under both situations. Modifying value m is presented to solve this protection-related problem. Minimum and maximum values of m are calculated to avoid overreach or blinding operation. After optimized by m, Zone II protection can trip correctly. Analysis and simulation results, based on two practical distribution systems, verified the effectiveness of the optimization strategy.
Magnetic anisotropy, damping, and interfacial spin transport in Pt/LSMO bilayers
Authors: Lee H. K. , Barsukov I. , Swartz A. G. , Kim B. , Yang L. , Hwang H. Y. , Krivorotov I. N.
Published: May 2016

We report ferromagnetic resonance measurements of magnetic anisotropy and damping in epitaxial La0.7Sr0.3MnO3 (LSMO) and Pt capped LSMO thin films on SrTiO3 (001) substrates. The measurements reveal large negative perpendicular magnetic anisotropy and a weaker uniaxial in-plane anisotropy that are unaffected by the Pt cap. The Gilbert damping of the bare LSMO films is found to be low α = 1.9(1) × 10−3, and two-magnon scattering is determined to be significant and strongly anisotropic. The Pt cap increases the damping by 50% due to spin pumping, which is also directly detected via inverse spin Hall effect in Pt. Our work demonstrates efficient spin transport across the Pt/LSMO interface.