bluuebunny/crossref_metadata_2025 huggingface dataset:
Serpentine geometry plasma actuators for flow control
Authors: Riherd Mark , Roy Subrata
Published: August 2013

In this paper, a curved class of plasma actuator geometries is presented. The intension of this paper is to extend the versatility of a dielectric barrier discharge plasma actuator by modifying the geometry of its electrodes, so that the plasma generated body force is able to excite a broader spectrum of flow physics than plasma actuators with a more standard geometry. Two examples of flow control are demonstrated numerically. An example of this class of actuators is shown to generate boundary layer streaks, which can be used to accelerate or delay the laminar to turbulent transition process, depending on how they are applied. Simulations of a low Reynolds number airfoil are also performed using additional examples of this class of actuators, where it is shown that this plasma actuator geometry is able to introduce energy into and excite a secondary instability mode and increase unsteady kinetic energy in the boundary layer. These two cases show that this general class of curved actuators possesses an increased versatility with respect to the standard geometry actuators.
The bond energy of ReO+: Guided ion-beam and theoretical studies of the reaction of Re+ (7S) with O2
Authors: Armentrout P. B.
Published: August 2013

The kinetic-energy dependence of the Re+ + O2 reaction is examined using guided ion-beam mass spectrometry. The cross section for ReO+ formation from ground state Re+ (7S) is unusual, exhibiting two endothermic features. The kinetic energy dependence for ReO+ formation is analyzed to determine D0(Re+‑O) = 4.82 ± 0.05 eV, with the higher energy feature having a threshold 1.35 ± 0.28 eV higher in energy. This bond energy is consistent with much less precise values determined in the literature. Formation of ReO2+ is also observed with a pressure dependent cross section, establishing that it is formed in an exothermic reaction of ReO+ with O2. The nature of the bonding for ReO+ and ReO2+ is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. The ground state of ReO+ is identified as either 5Π or 3Δ, with the latter favored once estimates of spin-orbit splitting are included. Bond energies for ground state ReO+ are calculated at this level as well as BP86 and CCSD(T,full) levels using several different basis sets. BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are lower, although estimated spin-orbit corrections increase the latter close to experiment. Potential energy surfaces for the reaction of Re+ with O2 are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Re+ (7S) inserts into O2 by forming a Re+(O2) (5A″) complex which can then couple with additional surfaces to form ground state ReO2+ (3B1). Several explanations for the unusual dual endothermic features are explored, with no unambiguous explanation being evident. As such, this heavy metal system provides a very interesting experimental phenomenon of both adiabatic and nonadiabatic behavior.
Dual-band infrared remote sensing system with combined long-wave infrared imaging and mid-wave infrared spectral analysis
Authors: Fang Zheng , Yi Xinjian , Liu Xiangyan , Zhang Wei , Zhang Tianxu
Published: August 2013

We present a new optical system for infrared (IR) image-spectrum integration remote sensing. The purpose to develop this instrument is to find the key spectral characteristics of typical hot target and to explore a new intelligence fusion method for the recognition. When mounted on a two-dimensional rotation stage, it can track the suspected target by image processing, and then get its spectrum to do recognition. It is a dual-band system with long-wave infrared (LWIR) imaging and mid-wave infrared (MWIR) spectrum. An IR dichroic beamsplitter is used to divide wideband incident infrared into LWIR and MWIR. Compared to traditional infrared combined imaging and spectral-analysis instruments, it yields higher sensitivity for measuring the IR spectrum. The sensors for imaging and spectrum detection are separate, so high spatial resolution, frame rate, and spectrum resolution can all be obtained simultaneously.
Aris-Taylor dispersion with drift and diffusion of particles on the tube wall
Authors: Berezhkovskii Alexander M. , Skvortsov Alexei T.
Published: August 2013

A laminar stationary flow of viscous fluid in a cylindrical tube enhances the rate of diffusion of Brownian particles along the tube axis. This so-called Aris-Taylor dispersion is due to the fact that cumulative times, spent by a diffusing particle in layers of the fluid moving with different velocities, are random variables which depend on the realization of the particle stochastic trajectory in the radial direction. Conceptually similar increase of the diffusivity occurs when the particle randomly jumps between two states with different drift velocities. Here we develop a theory that contains both phenomena as special limiting cases. It is assumed (i) that the particle in the flow can reversibly bind to the tube wall, where it moves with a given drift velocity and diffusivity, and (ii) that the radial and longitudinal diffusivities of the particle in the flow may be different. We derive analytical expressions for the effective drift velocity and diffusivity of the particle, which show how these quantities depend on the geometric and kinetic parameters of the model.
Three-manifold invariant from functional integration
Authors: Guadagnini Enore , Thuillier Frank
Published: August 2013

We give a precise definition and produce a path-integral computation of the normalized partition function of the Abelian U(1) Chern-Simons field theory defined in a general closed oriented 3-manifold. We use the Deligne-Beilinson formalism, we sum over the inequivalent U(1) principal bundles over the manifold and, for each bundle, we integrate over the gauge orbits of the associated connection 1-forms. The result of the functional integration is compared with the Abelian U(1) Reshetikhin-Turaev surgery invariant.
Reduction of edge localized mode intensity on DIII-D by on-demand triggering with high frequency pellet injection and implications for ITER
Authors: Baylor L. R. , Commaux N. , Jernigan T. C. , Meitner S. J. , Combs S. K. , Isler R. C. , Unterberg E. A. , Brooks N. H. , Evans T. E. , Leonard A. W. , Osborne T. H. , Parks P. B. , Snyder P. B. , Strait E. J. , Fenstermacher M. E. , Lasnier C. J. , Moyer R. A. , Loarte A. , Huijsmans G. T. A. , Futatani S.
Published: August 2013

The injection of small deuterium pellets at high repetition rates up to 12× the natural edge localized mode (ELM) frequency has been used to trigger high-frequency ELMs in otherwise low natural ELM frequency H-mode deuterium discharges in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. The resulting pellet-triggered ELMs result in up to 12× lower energy and particle fluxes to the divertor than the natural ELMs. The plasma global energy confinement and density are not strongly affected by the pellet perturbations. The plasma core impurity density is strongly reduced with the application of the pellets. These experiments were performed with pellets injected from the low field side pellet in plasmas designed to match the ITER baseline configuration in shape and normalized β operation with input heating power just above the H-mode power threshold. Nonlinear MHD simulations of the injected pellets show that destabilization of ballooning modes by a local pressure perturbation is responsible for the pellet ELM triggering. This strongly reduced ELM intensity shows promise for exploitation in ITER to control ELM size while maintaining high plasma purity and performance.
The interaction of 193-nm excimer laser radiation with single-crystal zinc oxide: The generation of atomic Zn line emission at laser fluences below breakdown
Authors: Khan Enamul H. , Langford S. C. , Dickinson J. T. , Boatner L. A.
Published: August 2013

The production of gas phase atomic and ionic line spectra accompanying the high laser fluence irradiation of solid surfaces is well known and is most often due to the production and interaction of high densities of atoms, ions, and electrons generated from laser-induced breakdown. The resulting plasma expands and moves rapidly away from the irradiated spot and is accompanied by intense emission of light. This type of “plume” is well studied and is frequently exploited in the technique of chemical analysis known as laser induced breakdown spectroscopy. Here, we describe a similar but weaker emission of light generated in vacuum by the laser irradiation of single crystal ZnO at fluences well below breakdown; this emission consists entirely of optical line emission from excited atomic Zn. We compare the properties of the resulting laser-generated gas-phase light emission (above and below breakdown) and describe a mechanism for the production of the low-fluence optical emission resulting from a fortuitous choice of material and laser wavelength.
The phase diagram of ice: A quasi-harmonic study based on a flexible water model
Authors: Ramírez R. , Neuerburg N. , Herrero C. P.
Published: August 2013

The phase diagram of ice is studied by a quasi-harmonic approximation. The free energy of all experimentally known ice phases has been calculated with the flexible q-TIP4P/F model of water. The only exception is the high pressure ice X, in which the presence of symmetric O−H−O bonds prevents its modeling with this empirical interatomic potential. The simplicity of our approach allows us to study ice phases at state points of the T–P plane that have been omitted in previous simulations using free energy methods based on thermodynamic integration. The effect in the phase diagram of averaging the proton disorder that appears in several ice phases has been studied. It is found particularly relevant for ice III, at least for cell sizes typically used in phase coexistence simulations. New insight into the capability of the employed water model to describe the coexistence of ice phases is presented. We find that the H-ordered ices IX and XIV, as well as the H-disordered ice XII, are particularly stable for this water model. This fact disagrees with experimental data. The unexpected large stability of ice IX is a property related to the TIP4P-character of the water model. Only after omission of these three stable ice phases, the calculated phase diagram becomes in reasonable qualitative agreement to the experimental one in the T–P region corresponding to ices Ih, II, III, V, and VI. The calculation of the phase diagram in the quantum and classical limits shows that the most important quantum effect is the stabilization of ice II due to its lower zero-point energy when compared to that one of ices Ih, III, and V.
The quest for self-consistency in hydrogen bond definitions
Authors: Prada-Gracia Diego , Shevchuk Roman , Rao Francesco
Published: August 2013

In the last decades several hydrogen-bond definitions were proposed by classical computer simulations. Aiming at validating their self-consistency on a wide range of conditions, here we present a comparative study of six among the most common hydrogen-bond definitions for temperatures ranging from 220 K to 400 K and six classical water models. Our results show that, in the interval of temperatures investigated, a generally weak agreement among definitions is present. Moreover, cutoff choice for geometrically based definitions depends on both temperature and water model. As such, analysis of the same water model at different temperatures as well as different water models at the same temperature would require the development of specific cutoff values. Interestingly, large discrepancies were found between two hydrogen-bond definitions which were recently introduced to improve on more conventional methods. Our results reinforce the idea that a more universal way to characterize hydrogen bonds in classical molecular systems is needed.
Control of tensile strain and interdiffusion in Ge/Si(001) epilayers grown by molecular-beam epitaxy
Authors: Luong T. K. P. , Dau M. T. , Zrir M. A. , Stoffel M. , Le Thanh V. , Petit M. , Ghrib A. , El Kurdi M. , Boucaud P. , Rinnert H. , Murota J.
Published: August 2013

Tensile-strained and n-doped Ge has emerged as a potential candidate for the realization of optoelectronic devices that are compatible with the mainstream silicon technology. Tensile-strained Ge/Si epilayers can be obtained by using the difference of thermal expansion coefficients between Ge and Si. We have combined various surface, structural, and compositional characterizations to investigate the growth mode and the strain state in Ge/Si epilayers grown by molecular-beam epitaxy. The Ge growth was carried out using a two-step approach: a low-temperature growth to produce relaxed and smooth buffer layers, which is followed by a high-temperature growth to get high quality Ge layers. The existence of a substrate temperature window from 260 to 300 °C is evidenced, which allows to completely suppress the Ge/Si Stranski-Krastanov growth. As a consequence of the high temperature growth, a tensile strain lying in the range of 0.22%–0.24% is obtained. Concerning the effect of thermal annealing, it is shown that cyclic annealing may allow increasing the tensile strain up to 0.30%. Finally, we propose an approach to use carbon adsorption to suppress Si/Ge interdiffusion, which represents one of the main obstacles to overcome in order to realize pure Ge-based optoelectronic devices.
Analysis and development of fourth order LCLC resonant based capacitor charging power supply for pulse power applications
Authors: Naresh P. , Hitesh C. , Patel A. , Kolge T. , Sharma Archana , Mittal K. C.
Published: August 2013

A fourth order (LCLC) resonant converter based capacitor charging power supply (CCPS) is designed and developed for pulse power applications. Resonant converters are preferred t utilize soft switching techniques such as zero current switching (ZCS) and zero voltage switching (ZVS). An attempt has been made to overcome the disadvantages in 2nd and 3rd resonant converter topologies; hence a fourth order resonant topology is used in this paper for CCPS application. In this paper a novel fourth order LCLC based resonant converter has been explored and mathematical analysis carried out to calculate load independent constant current. This topology provides load independent constant current at switching frequency (fs) equal to resonant frequency (fr). By changing switching condition (on time and dead time) this topology has both soft switching techniques such as ZCS and ZVS for better switching action to improve the converter efficiency. This novel technique has special features such as low peak current through switches, DC blocking for transformer, utilizing transformer leakage inductance as resonant component. A prototype has been developed and tested successfully to charge a 100 μF capacitor to 200 V.
Self-consistent model of polarization switching kinetics in disordered ferroelectrics
Authors: Genenko Yuri A. , Wehner Jens , von Seggern Heinz
Published: August 2013

A self-consistent two-dimensional model of polarization switching in polycrystalline ferroelectrics is developed. It accounts for the statistical distribution of the local switching times due to the random spatial field distribution as well as for the feedback effect of the depolarization field changing during the switching process. Thereby the polarization response of each single-crystalline grain is modeled in the spirit of the Kolmogorov-Avrami-Ishibashi model while the electric field in the system is evaluated by a finite-element method at every iteration step. The results exhibit fair agreement with experiments on bulk ferroelectrics.
Brain source localization: A new method based on MUltiple SIgnal Classification algorithm and spatial sparsity of the field signal for electroencephalogram measurements
Authors: Vergallo P. , Lay-Ekuakille A.
Published: August 2013

Brain activity can be recorded by means of EEG (Electroencephalogram) electrodes placed on the scalp of the patient. The EEG reflects the activity of groups of neurons located in the head, and the fundamental problem in neurophysiology is the identification of the sources responsible of brain activity, especially if a seizure occurs and in this case it is important to identify it. The studies conducted in order to formalize the relationship between the electromagnetic activity in the head and the recording of the generated external field allow to know pattern of brain activity. The inverse problem, that is given the sampling field at different electrodes the underlying asset must be determined, is more difficult because the problem may not have a unique solution, or the search for the solution is made difficult by a low spatial resolution which may not allow to distinguish between activities involving sources close to each other. Thus, sources of interest may be obscured or not detected and known method in source localization problem as MUSIC (MUltiple SIgnal Classification) could fail. Many advanced source localization techniques achieve a best resolution by exploiting sparsity: if the number of sources is small as a result, the neural power vs. location is sparse. In this work a solution based on the spatial sparsity of the field signal is presented and analyzed to improve MUSIC method. For this purpose, it is necessary to set a priori information of the sparsity in the signal. The problem is formulated and solved using a regularization method as Tikhonov, which calculates a solution that is the better compromise between two cost functions to minimize, one related to the fitting of the data, and another concerning the maintenance of the sparsity of the signal. At the first, the method is tested on simulated EEG signals obtained by the solution of the forward problem. Relatively to the model considered for the head and brain sources, the result obtained allows to have a significant improvement compared to the classical MUSIC method, with a small margin of uncertainty about the exact location of the sources. In fact, the constraints of the spatial sparsity on the signal field allow to concentrate power in the directions of active sources, and consequently it is possible to calculate the position of the sources within the considered volume conductor. Later, the method is tested on the real EEG data too. The result is in accordance with the clinical report even if improvements are necessary to have further accurate estimates of the positions of the sources.
A real-time algorithm for the harmonic estimation and frequency tracking of dominant components in fusion plasma magnetic diagnostics
Authors: Alves D. , Coelho R. ,   JET-EFDA Contributors
Published: August 2013

The real-time tracking of instantaneous quantities such as frequency, amplitude, and phase of components immerse in noisy signals has been a common problem in many scientific and engineering fields such as power systems and delivery, telecommunications, and acoustics for the past decades. In magnetically confined fusion research, extracting this sort of information from magnetic signals can be of valuable assistance in, for instance, feedback control of detrimental magnetohydrodynamic modes and disruption avoidance mechanisms by monitoring instability growth or anticipating mode-locking events. This work is focused on nonlinear Kalman filter based methods for tackling this problem. Similar methods have already proven their merits and have been successfully employed in this scientific domain in applications such as amplitude demodulation for the motional Stark effect diagnostic. In the course of this work, three approaches are described, compared, and discussed using magnetic signals from the Joint European Torus tokamak plasma discharges for benchmarking purposes.
A new quantum data processing inequality
Authors: Beigi Salman
Published: August 2013

Quantum data processing inequality bounds the set of bipartite states that can be generated by two far apart parties under local operations; having access to a bipartite state as a resource, two parties cannot locally transform it to another bipartite state with a mutual information greater than that of the resource state. But due to the additivity of quantum mutual information under tensor product, the data processing inequality gives no bound when the parties are provided with arbitrary number of copies of the resource state. In this paper, we introduce a measure of correlation on bipartite quantum states, called maximal correlation, that is not additive and gives the same number when computed for multiple copies. Then by proving a data processing inequality for this measure, we find a bound on the set of states that can be generated under local operations even when an arbitrary number of copies of the resource state is available.
Effects of unresolved satellite lines on lasing of extreme ultraviolet light with nitrogen plasma in a recombining phase
Authors: Tatsumura Nao , Yamamura Shuhei , Ozawa Takuya , Horioka Kazuhiko , Kawamura Tohru
Published: August 2013

Satellite lines with a high-lying spectator electron give unresolved spectral feature with respect to a parent resonance line. In our previous study [T. Ozawa et al., Phys. Plasmas 19, 063302 (2012)], population inversion between 3l and 2l of hydrogenlike nitrogen in a recombining phase was quantitatively estimated and the dielectronic-capture ladderlike processes, which implicitly include such doubly excited states as nln′l′ (n=2−4,n′≫n), were found to be indispensable in the estimation of a gain. In this study, the population densities of the doubly excited states are explicitly calculated by a time-dependent collisional-radiative model with desired plasma conditions for the lasing of nitrogen Balmer-α, which is a parent resonance line of unresolved satellite lines 3ln′l′→2ln′l′. The stimulated emission of the unresolved satellite lines caused by Balmer-α is found to reduce the population inversion between 3l and 2l, leading to essential saturation of the amplification of Balmer-α laser light.
Exact evaluation of the rates of electrostatic decay and scattering off thermal ions for an unmagnetized Maxwellian plasma
Authors: Layden B. , Cairns Iver H. , Robinson P. A.
Published: August 2013

Electrostatic decay of Langmuir waves into Langmuir and ion sound waves (L→L′+S) and scattering of Langmuir waves off thermal ions (L+i→L′+i′, also called “nonlinear Landau damping”) are important nonlinear weak-turbulence processes. The rates for these processes depend on the quadratic longitudinal response function α(2) (or, equivalently, the quadratic longitudinal susceptibility χ(2)), which describes the second-order response of a plasma to electrostatic wave fields. Previous calculations of these rates for an unmagnetized Maxwellian plasma have relied upon an approximate form for α(2) that is valid where two of the wave fields are fast (i.e., vϕ=ω/k≫Ve where ω is the angular frequency, k is the wavenumber, and Ve is the electron thermal speed) and one is slow (vϕ≪Ve). Recently, an exact expression was derived for α(2) that is valid for any phase speeds of the three waves in an unmagnetized Maxwellian plasma. Here, this exact α(2) is applied to the calculation of the three-dimensional rates for electrostatic decay and scattering off thermal ions, and the resulting exact rates are compared with the approximate rates. The calculations are performed using previously derived three-dimensional rates for electrostatic decay given in terms of a general α(2), and newly derived three-dimensional rates for scattering off thermal ions; the scattering rate is derived assuming a Maxwellian ion distribution, and both rates are derived assuming arc distributions for the wave spectra. For most space plasma conditions, the approximate rate is found to be accurate to better than 20%; however, for sufficiently low Langmuir phase speeds (vϕ/Ve≈3) appropriate to some spatial domains of the foreshock regions of planetary bow shocks and type II solar radio bursts, the use of the exact rate may be necessary for accurate calculations. The relative rates of electrostatic decay and scattering off thermal ions are calculated for a range of parameters using the exact expressions for the rates; electrostatic decay is found to have the larger growth rate over the whole range of parameters, consistent with previous approximate calculations.
Effect of diastolic flow patterns on the function of the left ventricle
Authors: Seo Jung Hee , Mittal Rajat
Published: August 2013

Direct numerical simulations are used to study the effect of intraventricular flow patterns on the pumping efficiency and the blood mixing and transport characteristics of the left ventricle. The simulations employ a geometric model of the left ventricle which is derived from contrast computed tomography. A variety of diastolic flow conditions are generated for a fixed ejection fraction in order to delineate the effect of flow patterns on ventricular performance. The simulations indicate that the effect of intraventricular blood flow pattern on the pumping power is physiologically insignificant. However, diastolic flow patterns have a noticeable effect on the blood mixing as well as the residence time of blood cells in the ventricle. The implications of these findings on ventricular function are discussed.
Ambipolar doping in SnO
Authors: Varley J. B. , Schleife A. , Janotti A. , Van de Walle C. G.
Published: August 2013

SnO is a promising oxide semiconductor that can be doped both p- and n-type, but the doping mechanisms remain poorly understood. Using hybrid functionals, we find that native defects cannot account for the unintentional p-type conductivity. Sn vacancies are shallow acceptors, but they have high formation energies and are unlikely to form. Unintentional impurities offer a more likely explanation for p-type doping; hydrogen is a likely candidate, and we find that it forms shallow-acceptor complexes with Sn vacancies. We also demonstrate that the ambipolar behavior of SnO can be attributed to the high position of the valence-band on an absolute energy scale.
External electric field effects on electronic and magnetic properties at molecule-metal interfaces: Cu-phthalocyanine adsorbed on Fe(001) surface
Authors: Liang S. H. , Tao L. L. , Liu D. P. , Han X. F.
Published: August 2013

We report the first-principles studies of adsorption of Cu-phthalocyanine (CuPc) molecules on Fe(001) surfaces using density functional theory with generalized gradient approximation. The van der Walls interaction between CuPc molecules and Fe surfaces was included with Grimme approximation. The detailed structural and electronic and magnetic properties at the interface between the CuPc and Fe(001) were obtained. More importantly, based on the understanding of adsorption configurations, we further studied the interfacial properties with considering the effect of external electric field. The results demonstrate that both the transferred charge and localized magnetic moments of adsorbed molecules can be tuned by external applied electric field.
Determination of open-circuit voltage in Cu(In,Ga)Se2 solar cell by averaged Ga/(In + Ga) near its absorber surface
Authors: Chantana J. , Murata M. , Higuchi T. , Watanabe T. , Teraji S. , Kawamura K. , Minemoto T.
Published: August 2013

The Cu(In,Ga)Se2 (CIGS) solar cells are fabricated, where CIGS absorbers with various Ga/III, Ga/(In + Ga), profiles are prepared by the so-called “multi-layer precursor method” using multi-layer co-evaporation of material sources. The dependence of cell parameters upon several averaged Ga/III ratios, calculated in different depth ranges of the Ga/III profiles from the absorber surfaces, is performed. It is revealed that open-circuit voltage (VOC) is mainly dependent on the averaged Ga/III, calculated near the surface area of the CIGS absorber (or in space charge region; SCR). The SCR width of ∼0.32 μm can be predicted, corresponding to the calculated value. Finally, the averaged Ga/III near the absorber surface is proposed as an indicator of VOC before solar cell fabrication, as long as carrier concentration is almost constant.
Excitation light source dependence of emission in Sn2+-Ce3+ codoped ZnO-P2O5 glasses
Authors: Masai Hirokazu , Hino Yusuke , Yanagida Takayuki , Fujimoto Yutaka , Fukuda Kentaro , Yoko Toshinobu
Published: August 2013

Correlation between excitation light source and the emission property of Sn2+-Ce3+ co-doped zinc phosphate glasses is examined. Although photoluminescence (PL) peaks of both Sn2+ and Ce3+ shifted with increasing amount of Ce3+, there was little energy resonance between Sn2+ and Ce3+ emission centers. On the other hand, radioluminescence (RL) spectra excited by X-ray was independent of the Ce concentration, indicating that emission was mainly observed from Sn2+ emission center. It is expected that energy relaxation process in a RL preferentially occurs in an ns2-type emission center that possesses high transition probability of the excited state in the higher energy region.
Effect of sodium incorporation into CuInSe2 from first principles
Authors: Oikkonen L. E. , Ganchenkova M. G. , Seitsonen A. P. , Nieminen R. M.
Published: August 2013

The presence of small amounts of sodium has been shown to improve the electronic performance of Cu(In,Ga)Se2 (CIGS) solar cells, but the origins of this effect have not yet been fully resolved. In this work, we have addressed the questions involving the role of sodium in CuInSe2 (CIS) using density-functional-theory-based calculations. We find no direct way how the creation of Na-related point defects in bulk CIS would enhance p-type conductivity. Instead, we demonstrate that Na reduces copper mass transport due to the capture of copper vacancies by NaCu defects. This finding provides an explanation for experimental measurements where the presence of Na has been observed to decrease copper diffusion. The suggested mechanism can also impede VCu-related cluster formation and lead to measurable effects on defect distribution within the material.
Atomic layer deposition of photoactive CoO/SrTiO3 and CoO/TiO2 on Si(001) for visible light driven photoelectrochemical water oxidation
Authors: Ngo Thong Q. , Posadas Agham , Seo Hosung , Hoang Son , McDaniel Martin D. , Utess Dirk , Triyoso Dina H. , Buddie Mullins C. , Demkov Alexander A. , Ekerdt John G.
Published: August 2013

Cobalt oxide (CoO) films are grown epitaxially on Si(001) by atomic layer deposition (ALD) using a thin (1.6 nm) buffer layer of strontium titanate (STO) grown by molecular beam epitaxy. The ALD growth of CoO films is done at low temperature (170–180  °C), using cobalt bis(diisopropylacetamidinate) and water as co-reactants. Reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional scanning transmission electron microscopy are performed to characterize the crystalline structure of the films. The CoO films are found to be crystalline as-deposited even at the low growth temperature with no evidence of Co diffusion into Si. The STO-buffered Si (001) is used as a template for ALD growth of relatively thicker epitaxial STO and TiO2 films. Epitaxial and polycrystalline CoO films are then grown by ALD on the STO and TiO2 layers, respectively, creating thin-film heterostructures for photoelectrochemical testing. Both types of heterostructures, CoO/STO/Si and CoO/TiO2/STO/Si, demonstrate water photooxidation activity under visible light illumination. In-situ X-ray photoelectron spectroscopy is used to measure the band alignment of the two heterojunctions, CoO/STO and CoO/TiO2. The experimental band alignment is compared to electronic structure calculations using density functional theory.
A generalized lumped element modeling of electrically and magnetically dual-tunable microwave magnetoelectric resonators
Authors: Zhou Hao-Miao , Li Chao , Zhu Feng-Jie , Qu Shao-Xing
Published: August 2013

According to the microwave transmission principle and the mechanism of ferromagnetic resonance (FMR), a generalized lumped element modeling for magnetoelectric tunable resonators based on the inverse magnetoelectric effect is established taking the impact of equivalent factors of piezoelectric layer into consideration. The lumped element modeling is used to analyze the electrically and magnetically dual-tunable FMR frequency drift of the magnetoelectric tunable resonator; the prediction results have a good agreement with the experimental results and the electromagnetic simulation results in quality and quantity. On this basis, this lumped element modeling is used to predict the effect of the applied electric field, the microstrip's width, the substrate's thickness, and the size of ferrite-piezoelectric layered structure on the ferromagnetic resonance. The results show that with the increase of applied electric field, the values of equivalent resistance R, inductor L, and turns ratio n increase slightly, while the value of C decreases slightly, the FMR frequency fr positively shifts; with the increase of the microstrip's width and substrate's thickness, the values of equivalent resistance R, inductor L, and turns ratio n decrease, while the value of C increases, the FMR bandwidth becomes narrower, and the ferromagnetic resonance attenuation becomes stronger at the same time. When the applied electric field is determined, with the increase of the length or thickness of layered structure, the FMR frequency shifts forward, the FMR peak point decreases first and then increases; with the width of layered structure increases, the FMR frequency of the resonator shifts backward, the FMR peak point decreases first and then increases.
Effect of concurrent Mg/Nb-doping on dielectric properties of Ba0.45Sr0.55TiO3 thin films
Authors: Alema Fikadu , Reich Michael , Reinholz Aaron , Pokhodnya Konstantin
Published: August 2013

Composition, microstructure, and dielectric properties of undoped and Ba(Mg1/3Nb2/3)O3 (BMN) doped Ba0.45Sr0.55TiO3 (BST) thin films deposited via rf. magnetron sputtering on platinized alumina substrates have been investigated. The analysis of microstructure has shown that despite the sizable effect of doping on the residual stress, the latter is partially compensated by the thermal expansion coefficient mismatch, and its influence on the BST film crystal structure is insignificant. It was revealed that BMN doped film demonstrated an average (over 2000 devices) of 52.5% tunability at 640 kV/cm, which is ∼8% lower than the value for the undoped film. This drop is associated with the presence of Mg ions in BMN; however, the effect of Mg doping is partially compensated by that of Nb ions. The decrease in grain size upon doping may also contribute to the tunability drop. Doping with BMN allows achievement of a compensation concentration yielding no free carriers and resulting in significant leakage current reduction when compared with the undoped film. In addition, the presence of large amounts of empty shallow traps related to NbTi• allows localizing free carriers injected from the contacts thus extending the device control voltage substantially above 10 V.
Indium oxide thin-film homo-junctions: Morphology and electrical properties
Authors: Stankiewicz Jolanta , Villuendas Francisco , Pilar Lozano María , Díez Isabel
Published: August 2013

Indium oxide shows an unusual combination of electrical and optical properties that give rise to a broad range of applications in optoelectronic devices. Here, we report results of structural, x–ray photoelectron spectroscopy, and electrical transport studies of transparent homo-junctions, obtained by sequential growth of polycrystalline thin layers of indium oxide under O2-rich and O2-poor conditions. We find that the growth temperature, which affects significantly film morphology, is critical for the rectifying behavior of the junctions. Only junctions grown at about 350 °C are rectifying. We also find that p-type–like layers have higher concentration of inter–grain oxygen than n-type layers, presumably coming from oxygen-rich deposition conditions and from much larger number of grain boundaries than in n-type layers. We conjecture that the segregation of oxygen ions at grain boundaries is responsible for the formation of inversion layers in O2-rich films and their apparent p-type dc conduction. This mechanism significantly modifies the capacitance–voltage characteristics of the junctions. However, the rectifying mechanism can be accounted for by a space-charge layer at the p-n interface. Such behavior might be important in other polycrystalline thin films with a large number of interface defects at grain boundaries.
Opposite signs of voltage-induced perpendicular magnetic anisotropy change in CoFeB|MgO junctions with different underlayers
Authors: Shiota Yoichi , Bonell Frédéric , Miwa Shinji , Mizuochi Norikazu , Shinjo Teruya , Suzuki Yoshishige
Published: August 2013

We report a voltage-induced perpendicular magnetic anisotropy (PMA) change in sputter-deposited Ta|CoFeB|MgO and Ru|CoFeB|MgO junctions. The PMA change is quantitatively evaluated by the field dependence of the tunneling magnetoresistance for various bias voltages. We find that both the sign and amplitude of the voltage effect depend on the underlayer, Ta or Ru, below the CoFeB layer. The rf voltage-induced ferromagnetic resonance spectra also support the underlayer-material-dependent direction of the voltage torque. The present study shows that the underlayer is one of the key parameters for controlling the voltage effect.
Efficiency enhancement calculations of state-of-the-art solar cells by luminescent layers with spectral shifting, quantum cutting, and quantum tripling function
Authors: ten Kate O. M. , de Jong M. , Hintzen H. T. , van der Kolk E.
Published: August 2013

Solar cells of which the efficiency is not limited by the Shockley-Queisser limit can be obtained by integrating a luminescent spectral conversion layer into the cell structure. We have calculated the maximum efficiency of state-of-the-art c-Si, pc-Si, a-Si, CdTe, GaAs, CIS, CIGS, CGS, GaSb, and Ge solar cells with and without an integrated spectral shifting, quantum cutting, or quantum tripling layer using their measured internal quantum efficiency (IQE) curves. Our detailed balance limit calculations not only take into account light in-coupling efficiency of the direct AM1.5 spectral irradiance but also wavelength dependence of the refractive index and the IQEs of the cells and the angular dependent light in-coupling of the indirect spectral irradiance. An ideal quantum cutting layer enhances all cell efficiencies ranging from a modest 2.9% for c-Si to much larger values of 4.0%, 7.7%, and 11.2% for CIGS, Ge, and GaSb, respectively. A quantum tripling layer also enhances cell efficiencies, but to a lesser extent. These efficiency enhancements are largest for small band gap cells like GaSb (7.5%) and Ge (3.8%). Combining a quantum tripling and a quantum cutting layer would enhance efficiency of these cells by a factor of two. Efficiency enhancement by a simple spectral shifting layer is limited to less than 1% in case the IQE is high for blue and UV lights. However, for CdTe and GaSb solar cells, efficiency enhancements are as high as 4.6% and 3.5%, respectively. A shifting layer based on available red LED phosphors like Sr2Si5N8:Eu will raise CdTe efficiency by 3.0%.
Bistability in droplet traffic at asymmetric microfluidic junctions
Authors: Parthiban Pravien , Khan Saif A.
Published: August 2013

We present the first experimental demonstration of confined microfluidic droplets acting as discrete negative resistors, wherein the effective hydrodynamic resistance to flow in a microchannel is reduced by the presence of a droplet. The implications of this hitherto unexplored regime in the traffic of droplets in microfluidic networks are highlighted by demonstrating bistable filtering into either arm of symmetric and asymmetric microfluidic loops, and programming oscillatory droplet routing therein.
New results in forecasting of photovoltaic systems output based on solar radiation forecasting
Authors: Fara Laurentiu , Bartok Blanka , Galbeaza Moraru Andrei , Oprea Cristian , Sterian Paul , Diaconu Alexandru , Fara Silvian
Published: August 2013

Accurate short term forecasting of photovoltaic (PV) systems output has a great significance for fast development of PV parks in South-East Europe, as well as in the case of Romania. Our approach on solar radiation forecast is based on two methods: autoregressive integrated moving average and artificial neural network. We have analyzed the daily solar irradiation variability and defined four synoptic situations to include the influence of cloudiness changes. Decadal variations of global solar radiation were also considered for long term forecast. The results were obtained using a database from Bucharest/Afumati Meteorological Station. We have developed an accurate forecasting model for a PV system's power output based on solar radiation forecasting results. By using complete datasets and including meteorological parameters such as cloudiness, relative humidity, air temperature, atmospheric pressure, and sunshine duration, as input for our model, we have managed to minimize forecasting errors and to obtain a more accurate forecast of the power output for the analyzed demo PV system.
Conditions for the spin wave nonreciprocity in an array of dipolarly coupled magnetic nanopillars
Authors: Verba Roman , Tiberkevich Vasil , Bankowski Elena , Meitzler Thomas , Melkov Gennadiy , Slavin Andrei
Published: August 2013

It is demonstrated that collective spin waves (SWs) propagating in complex periodic arrays of dipolarly coupled magnetic nanopillars existing in a saturated (single-domain) ground state in a zero bias magnetic field could be nonreciprocal. To guarantee the SW nonreciprocity, two conditions should be fulfilled: (i) existence of a nonzero out-of-plane component of the pillars' static magnetization and (ii) a complex periodicity of array's ground state with at least two elements per a primitive cell, if the elements are different, and at least three elements per a primitive cell, if the elements are identical.
Remarkable thermal conductivity reduction in metal-semiconductor nanocomposites
Authors: Shuvra Basu Tuhin , Yang Ronggui , Joottu Thiagarajan Suraj , Ghosh Siddhartha , Gierlotka Stanislaw , Ray Mallar
Published: August 2013

Remarkable reduction in thermal conductivity, by ∼2 orders of magnitude compared to the bulk counterpart, is observed in a metal-semiconductor nanocomposite consisting of silver (Ag) and silicon (Si) nanostructures. The variation of thermal conductivity with temperature and with volume fraction of metallic inclusion exhibits counter-intuitive behavior. Contrary to bulk composites, thermal conductivity decreases with the increase in the volume fraction of Ag nanocrystals (at least till 0.067 experimented) and increases with temperature over the range of 303-473 K. This remarkable reduction in the thermal conductivity of the nanocomposite is due to the interplay of size-dependent reduction in thermal conductivity of the individual nanostructures, increased contribution of phonon scattering at the interfaces between nanoparticles, and electron-phonon coupling inside metallic nanocrystals and across metal-semiconductor interface. Such hybrid metal-semiconductor nanostructures with reduced thermal conductivity offer immense potential for developing high efficiency thermoelectric materials.
Low voltage, high performance inkjet printed carbon nanotube transistors with solution processed ZrO2 gate insulator
Authors: Kim Bongjun , Jang Seonpil , Prabhumirashi Pradyumna L. , Geier Michael L. , Hersam Mark C. , Dodabalapur Ananth
Published: August 2013

High-performance single-walled carbon nanotube (SWCNT) thin-film transistors are fabricated by single-pass inkjet printing of SWCNTs on high-κ solution-processed ZrO2 gate dielectric. We demonstrate that an ultraviolet ozone treatment of the ZrO2 substrate is critical in achieving a uniform dispersion of sorted SWCNTs in the semiconducting channel. The resulting devices exhibit excellent performance with mobility and on/off current ratio exceeding 30 cm2 V−1 s−1 and 105, respectively, at low operating voltages (<5 V). The single-pass inkjet printing process demonstrated in this letter shows great promise as a reliable and scalable method for SWCNT based high performance electronics.
Eddy current pulsed phase thermography and feature extraction
Authors: He Yunze , Tian GuiYun , Pan Mengchun , Chen Dixiang
Published: August 2013

This letter proposed an eddy current pulsed phase thermography technique combing eddy current excitation, infrared imaging, and phase analysis. One steel sample is selected as the material under test to avoid the influence of skin depth, which provides subsurface defects with different depths. The experimental results show that this proposed method can eliminate non-uniform heating and improve defect detectability. Several features are extracted from differential phase spectra and the preliminary linear relationships are built to measure these subsurface defects' depth.
Iron-boron pair dissociation in silicon under strong illumination
Authors: Zhu Xiaodong , Yang Deren , Yu Xuegong , He Jian , Wu Yichao , Vanhellemont Jan , Que Duanlin
Published: August 2013

The dissociation of iron-boron pairs (FeB) in Czochralski silicon under strong illumination was investigated. It is found that the dissociation process shows a double exponential dependence on time. The first fast process is suggested to be caused by a positive Fe in FeB capturing two electrons and diffusion triggered by the electron-phonon interactions, while the second slow one would involve the capturing of one electron followed by temperature dependent dissociation with an activation energy of (0.21 ± 0.03) eV. The results are important for understanding and controlling the behavior of FeB in concentrator solar cells.
Magnetic thermal hysteresis due to paramagnetic-antiferromagnetic transition in Fe-24.4Mn-5.9Si-5.1Cr alloy
Authors: Wang L. , Cui Y. G. , Wan J. F. , Zhang J. H. , Rong Y. H.
Published: August 2013

Magnetic thermal hysteresis (MTH) associated with a paramagnetic (PM)-antiferromagnetic (AFM) phase transition was found in an Fe-24.4Mn-5.9Si-5.1Cr shape-memory alloy. Aside from the magnetic field (H), the driving rate (v) can also tune the critical temperature of the magnetic transition and cause an increase in MTH. The magnetic phase diagram obtained is discussed. The equation for MTH was deduced based on the Landau model for a PM-AFM transition that includes H and v dependence, which gives a reasonable account of the experimental results.