bluuebunny/crossref_metadata_2025 huggingface dataset:
Reliability and validity of an adapted Thai version of the Scoliosis Research Society-22 questionnaire
Authors: Leelapattana Pittavat , Keorochana Gun , Johnson Jared , Wajanavisit Wiwat , Laohacharoensombat Wichien
Published: December 2010

Purpose

The Scoliosis Research Society-22 (SRS-22) questionnaire is a widely accepted questionnaire used to assess the health-related quality of life for scoliosis patients in the United States. However, its adaptation in other languages is necessary for its multinational use. A cross-sectional study was performed to evaluate the validity and reliability of an adapted Thai version of the SRS-22 questionnaire.

Methods

An expert committee performed translation/retranslation of the English version of the SRS-22 questionnaire, as well as a cross-cultural adaptation process. Later, SRS-22 questionnaires and previously validated Short Form-36 version 2 (SF-36v2) outcome instruments were given to patients treated for idiopathic scoliosis with a minimum of 1 year of follow-up. Internal consistency and reproducibility were determined by Cronbach's alpha statistics and the intraclass correlation coefficient, respectively. Concurrent validity was measured by comparing SRS-22 results with a previously validated questionnaire (SF-36v2). Measurement was made using the Pearson correlation coefficient ( r).

Results

The study showed satisfactory internal consistency with Cronbach's alpha values for all of the corresponding domains (pain, 0.72; self-image/appearance, 0.87; mental health, 0.83; satisfaction with management, 0.63; and function/activity, 0.83). The test–retest reproducibility was also excellent or good for all domains (pain, 0.72; self-image/appearance, 0.85; mental health, 0.82; satisfaction, 0.62; and function/activity, 0.81). For concurrent validity, excellent correlation was found in two domains, good in six domains, moderate in five domains, and poor in five domains of the 18 relevant domains.

Conclusions

The Thai version of the SRS-22 outcome instrument has satisfactory internal consistency, excellent reproducibility, and acceptable validity.
Gun carrying by high school students in Boston, MA: Does overestimation of peer gun carrying matter?
Authors: Hemenway David , Vriniotis Mary , Johnson Renee M. , Miller Matthew , Azrael Deborah
Published: December 2010

This paper investigates: (1) whether high school students overestimate gun carrying by their peers, and (2) whether those students who overestimate peer gun carrying are more likely to carry firearms. Data come from a randomly sampled survey conducted in 2008 of over 1700 high school students in Boston, MA. Over 5% of students reported carrying a gun, 9% of boys and 2% of girls. Students substantially overestimated the percentage of their peers who carried guns; the likelihood that a respondent carried a gun was strongly associated with their perception of the level of peer gun carrying. Most respondents believed it was easier for other youth to obtain guns than it was for them. Social marketing campaigns designed to lower young people's perceptions about the prevalence of peer gun carrying may be a promising strategy for reducing actual gun carrying among youth.
Capsule dynamics and rheology in shear flow: Particle pressure and normal stress
Authors: Clausen Jonathan R. , Aidun Cyrus K.
Published: December 2010

In this paper, we examine the dynamics of an isolated capsule using a hybrid lattice-Boltzmann/finite-element method, with a focus on how the capsule dynamics affects the rheology of capsule suspensions. We study initially spherical capsules undergoing a “tank-treading” behavior in which the particle assumes an ellipsoidal shape at a steady orientation while the capsule’s membrane rotates. Of particular interest is the calculation of the particle pressure and a full characterization of the normal stresses. To date, results on capsule rheology only consider normal stress differences, which are insufficient to explain particle migration using the suspension balance model [P. R. Nott and J. F. Brady, “Pressure-driven suspension flow: Simulation and theory,” J. Fluid Mech. 275, 157 (1994)]. We also extend the results of R. Roscoe [“On the rheology of a suspension of viscoelastic spheres in a viscous liquid,” J. Fluid Mech. 28, 273 (1967)] using the solution for ellipsoidal particles of G. B. Jeffery [“The motion of ellipsoidal particles immersed in a viscous fluid,” Proc. R. Soc. London, Ser. A 102, 161 (1922)] to predict the particle-phase pressure of deformable particles. Both analytical modeling and numerical results show a negative (tensile) particle pressure, in contrast with the case of an isolated sphere, which shows no particle pressure.
Quantized Nambu–Poisson manifolds and n-Lie algebras
Authors: DeBellis Joshua , Sämann Christian , Szabo Richard J.
Published: December 2010

We investigate the geometric interpretation of quantized Nambu–Poisson structures in terms of noncommutative geometries. We describe an extension of the usual axioms of quantization in which classical Nambu–Poisson structures are translated to n-Lie algebras at quantum level. We demonstrate that this generalized procedure matches an extension of Berezin–Toeplitz quantization yielding quantized spheres, hyperboloids, and superspheres. The extended Berezin quantization of spheres is closely related to a deformation quantization of n-Lie algebras as well as the approach based on harmonic analysis. We find an interpretation of Nambu–Heisenberg n-Lie algebras in terms of foliations of \documentclass[12pt]{minimal}\begin{document}${\mathbbm{R}\!}^n$\end{document}Rn by fuzzy spheres, fuzzy hyperboloids, and noncommutative hyperplanes. Some applications to the quantum geometry of branes in M-theory are also briefly discussed.
Quasiclassical asymptotics and coherent states for bounded discrete spectra
Authors: Górska K. , Penson K. A. , Horzela A. , Duchamp G. H. E. , Blasiak P. , Solomon A. I.
Published: December 2010

We consider discrete spectra of bound states for nonrelativistic motion in attractive potentials \documentclass[12pt]{minimal}\begin{document}$V_{\sigma }(x) = -|V_{0}|\, |x|^{-\sigma },\, 0<\sigma \le 2$\end{document}Vσ(x)=−|V0||x|−σ,0<σ≤2. For these potentials the quasiclassical approximation for n → ∞ predicts quantized energy levels \documentclass[12pt]{minimal}\begin{document}$e_{\sigma }(n)$\end{document}eσ(n) of a bounded spectrum varying as \documentclass[12pt]{minimal}\begin{document}$e_{\sigma }(n) \sim -n^{-2\sigma /(2-\sigma )}$\end{document}eσ(n)∼−n−2σ/(2−σ). We construct collective quantum states using the set of wavefunctions of the discrete spectrum assuming this asymptotic behavior. We give examples of states that are normalizable and satisfy the resolution of unity, using explicit positive functions. These are coherent states in the sense of Klauder and their completeness is achieved via exact solutions of Hausdorff moment problems, obtained by combining Laplace and Mellin transform methods. For σ in the range 0 < σ ⩽ 2/3 we present exact implementations of such states for the parametrization σ = 2(k − l)/(3k − l) with k and l positive integers satisfying \documentclass[12pt]{minimal}\begin{document}$k>l$\end{document}k>l.
Experimental study of new laser-based alignment system at the KEK B-factory injector linear accelerator
Authors: Suwada T. , Satoh M. , Kadokura E.
Published: December 2010

A new laser-based alignment system for the precise alignment of accelerator components along an ideal straight line at the KEK B-factory injector linear accelerator (linac) is under development. This system is strongly required in the next generation of B-factories for the stable acceleration of high-brightness electron and positron beams with high bunch charges and also for maintaining the stability of injection beams with high quality. A new laser optics for the generation of a so-called Airy beam has been developed for the laser-based alignment system. The laser propagation characteristics both in vacuum and at atmospheric pressure have been systematically investigated in an 82-m-long straight section of the injector linac. The laser-based alignment measurements based on the new laser optics have been carried out with a measurement resolution of ±0.1 mm level by using an existing laser detection electronics. The horizontal and vertical displacements from a reference laser line measured using this system are in good agreement with those measured using a standard telescope-based optical alignment technique. In this report, we describe the experimental study in detail along with the basic designs and the recent developments in the new laser-based alignment system.
Phase sensitive absolute amplitude detection of surface vibrations using homodyne interferometry without active stabilization
Authors: Lipiäinen Lauri , Kokkonen Kimmo , Kaivola Matti
Published: December 2010

A detection scheme for obtaining phase and absolute amplitude information of surface vibrations on microacoustic components using homodyne laser interferometry is described. The scheme does not require active stabilization of the optical path length of the interferometer. The detection setup is realized in a homodyne Michelson interferometer configuration, and selected measurements on a 374 MHz surface acoustic wave fan-shaped filter and two different piezoelectrically actuated micromechanical resonators are presented to demonstrate the performance of the instrument. With the current detection electronics, the interferometer is capable of detecting out-of-plane surface vibrations up to 2 GHz with a lateral resolution of better than 1 μm and with a minimum detectable vibration amplitude of ∼1 pm.
Interchannel optical coupling within arrays of linear microplasmas generated in 25–200μm wide glass channels
Authors: Sung S. H. , Hwang I. C. , Park S.-J. , Eden J. G.
Published: December 2010

Axially uniform microcavity plasmas with widths of 25–200 μm and aspect ratios as high as 500 have been generated in glass microchannels. Sealed in cavities 2.5 cm in length and having a cross-sectional area of 2.5×102–104 μm2, these microplasmas operate in the abnormal glow regime with neutral particle temperatures of 365–420 K when the rare gas pressure is 200–700 Torr. In arrays as large as ten parallel microchannel plasmas, evidence of optical coupling among the channels is observed in the form of strongly enhanced atomic emission which is attributed to electron heating driven by the resonant absorption of scattered radiation.
Five-dimensional SU(2) AGT conjecture and recursive formula of deformed Gaiotto state
Authors: Yanagida Shintarou
Published: December 2010

This paper deals with the five-dimensional pure SU(2) Alday-Gaiotto-Tachikawa (AGT) conjecture proposed by Awata and Yamada [J. High. Energy Phys. 1001, 125 (2010)]. We give a conjecture on a recursive formula for the inner product of the deformed Gaiotto state. We also show that the K-theoretic pure SU(2) Nekrasov partition function satisfies the same recursion relation. Therefore the five-dimensional AGT conjecture is reduced to our conjectural recursive formula.
Ordered equilibrium structures of soft particles in thin layers
Authors: Kahn Mario , Weis Jean-Jacques , Kahl Gerhard
Published: December 2010

Considering a system of Gaussian particles confined between two hard, parallel plates, we investigate at T = 0, ordered equilibrium configurations that the system forms as the distance D between the plates gradually increases. Using a very sensitive and reliable optimization technique that is based on ideas of genetic algorithms, we are able to identify the emerging sequences of the energetically most favorable structures. Although the resulting phase diagram is rather complex, its essential features can be reduced to the discussion of two archetypes of structural transitions: (i) a continuous transformation at a fixed number of layers, leading from a square to a centered rectangular and then to a hexagonal lattice; (ii) a discontinuous transition, transforming a hexagonal to a square lattice via complex intermediate structures, i.e., the so-called buckling transition, which is encountered as the system forms a new layer. Detailed Monte Carlo simulations are able to confirm the theoretical predictions on a semiquantitative level but are not able to grasp the tiny energetic differences between competing structures.
Morphological classification and quantitative analysis of etch pits
Authors: Motzer C. , Reichling M.
Published: December 2010

Etch pits created by hydrochloric and phosphoric acid on cleaved CaF2(111) are investigated by scanning force microscopy (SFM). A geometric and dimensional analysis of the etch pits reveals two distinctly different types. Type-I etch pits evolve at dislocation defects, are pointed and their size and eccentricity is related to the angle between the dislocation and the surface. Type-II etch pits result from defects below the surface, are flat-bottomed for longer etching times and exhibit a characteristic ratio of depth and edge length depending on the type of etchant. An analysis of etch pit morphology allows an identification of the origin of an etch pit and a characterization of the associated defect structure.
Non-Born–Oppenheimer approximation for very weakly bound states of molecular anions
Authors: Garrett W. R.
Published: December 2010

The influence of nuclear rotation on weak electron binding in the long range field of a linear polar molecule is treated in a way that leads ultimately, with suitable approximation, to the familiar equations for close coupling of electron-nuclear-rotational motions. Subsequently, a conventional pseudopotential approximation is invoked to examine the rotational spectra of HCN and DCN anions. It is shown that the number of rotationally excited anion states cannot be reliably predicted by assuming that zero binding occurs when the rotational energy equals the electron affinity obtained in the Born–Oppenheimer approximation. A method is suggested for combining accurate molecular orbital and parameterized pseudopotential methods to provide accurate electron affinities for very weakly bound anionic states.
Influence of the magnetic field on phase transitions in PrAlO3
Authors: Filipič C. , Bobnar V. , Turczynski S. , Pawlak D. A. , Wencka M. , Dolinšek J. , Levstik A.
Published: December 2010

Dielectric properties of PrAlO3 single crystals were studied under the influence of the magnetic field of 0.8 T. Below 300 K all phase transitions detected previously with different experimental methods are observed in ε′[001](T) and ε′[11¯0](T). The phase transition at 152 K is of the first order and under the influence of magnetic field the thermal hysteresis increases.
Atomistic theory of amyloid fibril nucleation
Authors: Cabriolu Raffaela , Kashchiev Dimo , Auer Stefan
Published: December 2010

We consider the nucleation of amyloid fibrils at the molecular level when the process takes place by a direct polymerization of peptides or protein segments into β-sheets. Employing the atomistic nucleation theory (ANT), we derive a general expression for the work to form a nanosized amyloid fibril (protofilament) composed of successively layered β-sheets. The application of this expression to a recently studied peptide system allows us to determine the size of the fibril nucleus, the fibril nucleation work, and the fibril nucleation rate as functions of the supersaturation of the protein solution. Our analysis illustrates the unique feature of ANT that the size of the fibril nucleus is a constant integer in a given supersaturation range. We obtain the ANT nucleation rate and compare it with the rates determined previously in the scope of the classical nucleation theory (CNT) and the corrected classical nucleation theory (CCNT). We find that while the CNT nucleation rate is orders of magnitude greater than the ANT one, the CCNT and ANT nucleation rates are in very good quantitative agreement. The results obtained are applicable to homogeneous nucleation, which occurs when the protein solution is sufficiently pure and/or strongly supersaturated.
Understanding mixing of Ni and Pt in the Ni/Pt(111) bimetallic catalyst via molecular simulation and experiments
Authors: Wang Hangyao , Stamatakis Michail , Hansgen Danielle A. , Caratzoulas Stavros , Vlachos Dionisios G.
Published: December 2010

Molecular dynamics (MD) simulations employing embedded atom method potentials and ultrahigh vacuum (UHV) experiments were carried out to study the mixing process between the Ni and Pt atoms in the Ni/Pt(111) bimetallic system. The barrier for a Ni atom to diffuse from the top surface to the subsurface layer is rather high (around 1.7 eV) as calculated using the nudged elastic band (NEB) method. Analysis of the relaxation dynamics of the Ni atoms showed that they undergo diffusive motion through a mechanism of correlated hops. At 600 K, all Ni atoms remain trapped on the top surface due to large diffusion barriers. At 900 K, the majority of Ni atoms diffuse to the second layer and at 1200 K diffusion to the bulk is observed. We also find that smaller Ni coverages and the presence of Pt steps facilitate the Ni–Pt mixing. By simulated annealing simulations, we found that in the mixed state, the Ni fraction oscillates between layers, with the second layer being Ni-richer at equilibrium. The simulation results at multiple time scales are consistent with the experimental data.
From amorphous to microcrystalline: Phase transition in rapid synthesis of hydrogenated silicon thin film in low frequency inductively coupled plasmas
Authors: Xiao S. Q. , Xu S. , Wei D. Y. , Huang S. Y. , Zhou H. P. , Xu Y.
Published: December 2010

Hydrogenated silicon (Si:H) thin films were fabricated on glass substrates by low frequency inductively coupled plasma-assisted chemical vapor deposition using a silane precursor with low hydrogen dilution at room temperature. The crystallinity and microstructure properties of the Si:H thin films deposited at different inductive radio-frequency (rf) power density were systematically studied by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. We found that at a low rf power density of 16.7 to 20.8 mW/cm3, the structure of silicon thin films evolves from a completely amorphous phase to an intermediate phase containing both amorphous and microcrystalline silicon. As the power density is increased to a moderate value of 25 mW/cm3, a highly crystallized (111)-preferred hydrogenated microcrystalline silicon (μc-Si:H) film featuring a vertically aligned cone-shaped structure, is emerging. Both the crystallinity and deposition rate exhibit a monotonic increase with the increase in the rf power density, reaching a maximum value of 85% and 1.07 nm/s, respectively, at a power density of 41.7 mW/cm3. Scanning electron microscopy reveals that continuous and dense μc-Si:H films with grain size of tens to hundreds nanometers can be achieved deterministically without the formation of amorphous incubation layer, and this is of great importance for synthesis of multilayer structures in p-i-n solar cells. The formation mechanism of the μc-Si:H films and the elimination of the amorphous incubation layer are explained in terms of the high electron density and the plasma-surface interactions.
Study of the epitaxial relationships between III-nitrides and M-plane sapphire
Authors: Vennéguès Philippe , Zhu Tiankai , Martin Denis , Grandjean Nicolas
Published: December 2010

GaN films epitaxially-grown on M-sapphire may have different orientations, either nonpolar and semipolar. In this paper, the different epitaxial relationships are investigated in details thanks to transmission electron microscopy. It is shown that these relationships drastically depend on the nitridation conditions. Mechanisms explaining the different epitaxial relationships are proposed. These mechanisms take into account the formation of a nitridation layer, the lattice mismatches between the growing films, and the substrate, and the surface energies. It is, moreover, shown that the difference of symmetries between the M-sapphire surface and the epitaxial films leads to the formation of growth twins for the (101¯0) and (101¯3¯) orientations.
Simulation of thermal conductance across dimensionally mismatched graphene interfaces
Authors: Huang Zhen , Fisher Timothy S. , Murthy Jayathi Y.
Published: December 2010

This paper considers phonon transport behavior in graphene nanoribbons (GNRs) that bridge semi-infinite graphene contacts. The work employs an atomistic Green’s function (AGF) method to investigate phonon wave effects in GNRs with both zigzag and armchair edges. Thermal conductances are found to be sensitive to the edge shape of the ribbons; a sandwiched zigzag GNR structure has almost twice the thermal conductance of the corresponding armchair structure. Results show that the graphene/GNR interface moderately reduces phonon conductance compared to a freestanding GNR. At fixed device lengths, conductance increases with the width of GNR. On the other hand, conductance decreases with GNR length. The zigzag ribbons show smaller reduction upon increasing of GNR length than armchair ribbons; the conductances of both ribbons converge to a length-independent value. For very short devices, thermal conductance can exceed that of a single graphene-GNR interface.
Transition of equilibrium stochastic to unidirectional velocity vectors in a nanowire subjected to a towering electric field
Authors: Arora Vijay K. , Chek Desmond C. Y. , Tan Michael L. P. , Hashim Abdul Manaf
Published: December 2010

The equilibrium Fermi–Dirac distribution is revealed to transform to an asymmetric distribution in a very high electric field where the energy gained (or lost) in a mean free path is of paramount importance. The equilibrium stochastic velocity vectors randomly oriented in and opposite to the quasifree direction of a nanowire are shown to streamline in the presence of an extremely high electric field. The complete velocity-field characteristics are acquired. The ultimate directed drift velocity in a towering field is shown to be limited to the appropriately averaged Fermi velocity in the strongly degenerate limit where only half of the quantum states are accessible to electrons. This unidirectional velocity does not sensitively depend on the low-field Ohmic mobility. The emission of a quantum in the form of a phonon or photon lowers the saturation velocity from its ultimate unidirectional limit.
Microstructural and dielectric properties of Ba0.6Sr0.4Ti1−xZrxO3 based combinatorial thin film capacitors library
Authors: Liu Guozhen , Wolfman Jérôme , Autret-Lambert Cécile , Sakai Joe , Roger Sylvain , Gervais Monique , Gervais François
Published: December 2010

Epitaxial growth of Ba0.6Sr0.4Ti1−xZrxO3 (0≤x≤0.3) composition spread thin film library on SrRuO3/SrTiO3 layer by combinatorial pulsed laser deposition (PLD) is reported. X-ray diffraction and energy dispersive x-ray spectroscopy studies showed an accurate control of the film phase and composition by combinatorial PLD. A complex evolution of the microstructure and morphology with composition of the library is described, resulting from the interplay between epitaxial stress, increased chemical pressure, and reduced elastic energy upon Zr doping. Statistical and temperature-related capacitive measurements across the library showed unexpected variations in the dielectric properties. Doping windows with enhanced permittivity and tunability are identified, and correlated to microstructural properties.
Persistent currents, flux quantization, and magnetomotive forces in normal metals and superconductors (Review Article)
Authors: Kulik I. O.
Published: December 2010

The notion of persistent current goes back to orbital currents in normal metals, semiconductors and even insulators displaying diamagnetic behavior in weak magnetic fields, but has come to focus on the discovery of current persistence and magnetic flux quantization in high fields in atomically large, but macroscopically small (mesoscopic) objects. This phenomenon has many similarities with supercurrents in superconducting metals. Here we review progress in our understanding of the physical and technological aspects of this phenomenon. Exact solutions for currents, magnetic moments and magnetomotive forces (torques) in crossed magnetic fields are presented. Time-dependent phenomena in crossed magnetic and electric fields, and the possibility of spontaneous persistent currents and the extraction of work from static and dynamic quantum states, are also discussed.
Theory of oscillations in STM conductance caused by subsurface defects (Review Article)
Authors: Avotina Ye. S. , Kolesnichenko Yu. A. , van Ruitenbeek J. M.
Published: December 2010

In this review we discuss recent theoretical studies of single subsurface defects by means of a scanning tunneling microscope (STM). These investigations are based on quantum interference effects between the electron partial waves that are directly transmitted through the contact and the partial waves scattered by a defect. In particular, we demonstrate the feasibility of imaging the position of a defect below a metal surface by means of STM. Different types of subsurface defects are discussed: point-like magnetic and nonmagnetic defects, magnetic clusters in a nonmagnetic host metal, and nonmagnetic defects in an s-wave superconductor. The effect of Fermi surface anisotropy is analyzed. Studies of the effect of high magnetic fields on the STM conductance of tunnel point contacts in the presence of a single defect are also discussed.
The direct problem of acoustic diffraction of an audible probe radiation by an air-saturated porous cylinder
Authors: Ogam Erick , Depollier Claude , Fellah Z. E. A.
Published: December 2010

Gas-saturated, solid skeleton, porous media like geomaterials, polymeric and metallic foams or biomaterials are fundamental in a diverse range of applications, from structural materials to energy technologies. Most polymeric foams are used for noise control applications and knowledge of the manner in which the energy of sound waves is dissipated with respect to the intrinsic acoustic properties is important for the design of sound packages. Foams are often employed in the audible, low frequency range where modeling and measurement techniques for the recovery of physical parameters responsible for energy loss, are still few. Accurate acoustic methods for the characterization of porous media are based on the measurement of the transmitted and/or reflected acoustic waves by platelike specimens at ultrasonic frequencies. In this study we have developed a method based on the theory and experiment of diffraction of acoustic waves by a rigid-frame, air-saturated polymeric foam in cylindrical form in the audible frequency regime. A dispersion relation for sound wave propagation in the porous medium is derived from the propagation equations and a model solution is sought based on plane-wave decomposition using orthogonal cylindrical functions. The explicit analytical solution equation of the scattered field show that it is also dependent on the intrinsic microstructural parameters of the porous cylinder namely, porosity, tortuosity, and the flow resistivity (related to permeability).
The discharge plasma in ion engine neutralizers: Numerical simulations and comparisons with laboratory data
Authors: Mikellides Ioannis G. , Goebel Dan M. , Snyder John Steven , Katz Ira , Herman Daniel A.
Published: December 2010

Numerical simulations of neutralizer hollow cathodes at various operating conditions and orifice sizes are presented. The simulations were performed using a two-dimensional axisymmetric model that solves numerically an extensive system of conservation laws for the partially ionized gas in these devices. The results for the plasma are compared directly with Langmuir probe measurements. The computed keeper voltages are also compared with the observed values. Whenever model inputs and/or specific physics of the cathode discharge were uncertain or unknown additional sensitivity calculations have been performed to quantify the uncertainties. The model has also been employed to provide insight into recent ground test observations of the neutralizer cathode in NASA’s evolutionary xenon thruster. It is found that a likely cause of the observed keeper voltage drop in a long duration test of the engine is cathode orifice erosion.
Microstructure and ferroic properties of epitaxial [γ-Fe2O3–BiFeO3]−Bi3.25La0.75Ti3O12 composite bilayers
Authors: Gautreau O. , Harnagea C. , Gunawan L. , Botton G. A. , Pintilie L. , Singh M. P. , Pignolet A.
Published: December 2010

Epitaxial [γ-Fe2O3–BiFeO3]/Bi3.25La0.75Ti3O12 and Bi3.25La0.75Ti3O12/[γ-Fe2O3–BiFeO3] composite bilayers were grown on SrRuO3 coated (111) SrTiO3 substrates in order to investigate the influence of the morphology of the γ-Fe2O3–BiFeO3 self assembled nanocomposite layer on the multiferroic properties of the bilayer. Both types of bilayers exhibit high resistivity and simultaneously ferroelectricity and ferrimagnetism at room temperature. When the γ-Fe2O3–BiFeO3 composite layer is sandwiched between the Bi3.25La0.75Ti3O12 film and the substrate, the BiFeO3 component is not only subjected to epitaxial strain induced by the surface on top of which it grows but also to elastic interactions with the Bi3.25La0.75Ti3O12 capping layer. The latter indeed reduce the amount of γ-Fe2O3 inclusions, affects the morphology of the grains in the γ-Fe2O3–BiFeO3 layer, and increases the shape anisotropy of the γ-Fe2O3 inclusions. Additionally, this modification in the microstructure of the γ-Fe2O3–BiFeO3 layer induces an imprint in the ferroelectric hysteresis loop as well as a decrease in the saturation magnetization, and its magnetic easy axis direction changes from in-plane to out-of plane.
Structures of tin cluster cations $\rm {Sn_{3}}^+$ Sn 3+ to $\rm {Sn_{15}}^+$ Sn 15+
Authors: Drebov Nedko , Oger Esther , Rapps Thomas , Kelting Rebecca , Schooss Detlef , Weis Patrick , Kappes Manfred M. , Ahlrichs Reinhart
Published: December 2010

We employ a combination of ion mobility measurements and an unbiased systematic structure search with density functional theory methods to study structure and energetics of gas phase tin cluster cations, \documentclass[12pt]{minimal}\begin{document}$\rm {Sn_{n}}^+$\end{document} Sn n+, in the range of n = 3–15. For \documentclass[12pt]{minimal}\begin{document}$\rm {Sn_{13}}^+$\end{document} Sn 13+ we also carry out trapped ion electron diffraction measurements to ascertain the results obtained by the other procedures. The structures for the smaller systems are most easily described by idealized point group symmetries, although they are all Jahn–Teller distorted: \documentclass[12pt]{minimal}\begin{document}$\rm D_{3h}$\end{document}D3h (trigonal bipyramid), \documentclass[12pt]{minimal}\begin{document}$\rm D_{4h}$\end{document}D4h (octahedron), \documentclass[12pt]{minimal}\begin{document}$\rm D_{5h}$\end{document}D5h (pentagonal bipyramid) for n = 5, 6, and 7. For the larger systems we find capped \documentclass[12pt]{minimal}\begin{document}$\rm D_{5h}$\end{document}D5h for \documentclass[12pt]{minimal}\begin{document}$\rm {Sn_{8}}^+$\end{document} Sn 8+ and \documentclass[12pt]{minimal}\begin{document}$\rm {Sn_{9}}^+$\end{document} Sn 9+, \documentclass[12pt]{minimal}\begin{document}$\rm D_{3h}$\end{document}D3h (tricapped trigonal prism) and \documentclass[12pt]{minimal}\begin{document}$\rm D_{4d}$\end{document}D4d (bicapped squared antiprism) plus adatoms for n = 10, 11, 14, and 15. A centered icosahedron with a peripheral atom removed is the dominant motif in \documentclass[12pt]{minimal}\begin{document}$\rm {Sn_{12}}^+$\end{document} Sn 12+. For \documentclass[12pt]{minimal}\begin{document}$\rm {Sn_{13}}^+$\end{document} Sn 13+ the calculations predict a family of virtually isoenergetic isomers, an icosahedron and slightly distorted icosahedra, which are about 0.25 eV below two \documentclass[12pt]{minimal}\begin{document}$\rm C_1$\end{document}C1 structures. The experiments indicate the presence of two structures, one from the \documentclass[12pt]{minimal}\begin{document}$\rm I_h$\end{document}Ih family and a prolate \documentclass[12pt]{minimal}\begin{document}$\rm C_1$\end{document}C1 isomer based on fused deltahedral moieties.
Quantum behavior of a flux qubit coupled to a resonator
Authors: Omelyanchouk A. N. , Shevchenko S. N. , Greenberg Ya. S. , Astafiev O. , Il’ichev E.
Published: December 2010

A detailed theory for a system of a superconducting qubit coupled to a transmission line resonator is presented. We describe the system by solving analytically and numerically the master equation for the density matrix, which includes a dissipative Lindblad term. We calculate the transmission coefficient, which provides a way to probe the dressed states of a qubit. The theoretical results are related to experiments with intermediate coupling between a qubit and a resonator when the coupling energy is of the same order as the qubit relaxation rate.
Voltage-driven superconducting weak link as a refrigerator for cooling of nanomechanical vibrations
Authors: Sonne G. , Peña-Aza M. E. , Shekhter R. I. , Gorelik L. Y. , Jonson M.
Published: December 2010

We consider a new type of cooling mechanism for a suspended nanowire acting as a weak link between two superconductive electrodes. By applying a bias voltage over the system, we show that the system can be viewed as a refrigerator for the nanomechanical vibrations, where energy is continuously transferred from the vibrational degrees of freedom to the extended quasiparticle states in the leads through the periodic modulation of the inter-Andreev level separation. The necessary coupling between the electronic and mechanical degrees of freedom responsible for this energy-transfer can be achieved both with an external magnetic or electrical field, and is shown to lead to an effective cooling of the vibrating nanowire. Using realistic parameters for a suspended nanowire in the form of a metallic carbon nanotube we analyze the evolution of the density matrix and demonstrate the possibility of cooling the system down to a stationary vibron population of ∼0.1. Furthermore, it is shown that the stationary occupancy of the vibrational modes of the nanowire can be directly probed using the dc current responsible for carrying away the absorbed energy from the vibrating nanowire.
Theory of quantum transport in Josephson junctions with a ferromagnetic insulator
Authors: Kawabata Shiro , Asano Yasuhiro
Published: December 2010

We investigate Josephson transport through ferromagnetic insulators (FIs) taking the band structure of the FIs explicitly into account. Using a recursive Green function method, we find that a π-junction is formed in this type of system. Moreover, an atomic-scale 0–π oscillation is induced by increasing the thickness of an FI and its oscillation period is universal, exactly equal to a single atomic layer. Based on these results, we show that a stable π-state can be realized in junctions based on high-Tc superconductors with a La2BaCuO5 barrier. Such FI-based Josephson junctions may become an element in the architecture of future quantum computers.
Shock-induced cation disorder in magnesium aluminate spinel
Authors: Chen Q. Y. , Meng C. M. , Lu T. C. , Xu M. , Qi J. Q. , Tan J. J.
Published: December 2010

An increase in lattice constants and an order–disorder phase transition were observed in the magnesium aluminate spinel (MgAl2O4) powders after shock compression. Theoretical calculations on the basis of density functional theory confirm that the remarkable volume expansion in shocked MgAl2O4 powders is closely related to the substantial site disorder in the MgAl2O4 lattice. The calculations also show that the partially inverse MgAl2O4 spinel with an inversion index of 0.7 represents the greatest disordered metastable phase and the most unstable structure.
Systematic study of the effect of La2O3 incorporation on the flatband voltage and Si band bending in the TiN/HfO2/SiO2/p-Si stack
Authors: Di Ming , Bersch Eric , Clark Robert D. , Consiglio Steven , Leusink Gert J. , Diebold Alain C.
Published: December 2010

Recent studies have shown that La2O3 films can be used to adjust the threshold voltage (Vt) of NMOS Hf-based high-k/metal gate devices to desirable values, and a dipole at the high-k/SiO2 interface has been proposed to explain the Vt shifts. In order to investigate the mechanism of the Vt shift further, we have measured the flatband voltage (Vfb) and Si band bending of technologically relevant TiN/HfO2/La2O3/SiO2/p-Si stacks where the thickness and position of the La2O3 layer have been systematically varied. We observed systematic changes in Vfb, Si band bending and the HfO2-Si valence band offset as a function of La2O3 layer thickness and position. These changes can be explained by a band alignment model that includes a dipole at the high-k/SiO2 interface, thus supporting the work of previous authors. In addition, we have derived the theoretical relationship between Vfb and Si band bending, which agrees well with our experimental measurements.
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ion-exchanged sodium magnesium aluminum germanate glass waveguide amplifier operating in the first telecommunications window
Authors: Yang Dianlai , Zhang Jie , Pun Edwin Yue-Bun , Lin Hai
Published: December 2010

Potassium-sodium (K+−Na+) ion-exchanged multimode channel waveguide amplifiers have been fabricated based on Tm3+/Yb3+ codoped sodium magnesium aluminum germanate (NMAG) glass substrates. The normalized optical and relative gain coefficients of a 2.20 cm long device were identified to be 3.65 dB/cm and 1.58 dB/cm, respectively, at a signal wavelength of 810 nm under 457 mW 980 nm laser diode excitation. These are the highest values reported, and the results indicate that Tm3+/Yb3+ codoped NMAG glasses are an attractive material for optical amplification in the first telecommunications window.
Application of positron annihilation and Raman spectroscopies to the study of perovskite type materials
Authors: Grebennikov D. , Ovchar O. , Belous A. , Mascher P.
Published: December 2010

Defect properties of perovskite type materials, Ba3B′Nb2O9 (where B′=Mg, Zn, or Co), with near-stoichiometric compositions were studied by positron annihilation and Raman spectroscopies. Theoretical simulations of stoichiometric perovskites revealed a dependence of the positron bulk lifetime on the degree of ordering. In Ba3MgNb2O9 (BMN) the positron bulk lifetime for a completely disordered structure is 195 ps versus 237 ps for a completely ordered one. The predicted bulk lifetimes for Ba3ZnNb2O9 (BZN) and Ba3CoNb2O9 (BCN), with Pm3¯m symmetries are 193 ps and 194 ps, respectively. It was found that deviation from stoichiometry results in the appearance of secondary Ba- and Nb-rich phases, which according to theoretical simulations have bulk lifetimes much longer than that of the host material. Positron lifetime spectroscopy was used to monitor changes in the concentration of these second phases. The difference between predicted defect lifetimes and the bulk values for the studied perovskites was less than 70 ps. This and the likely small concentrations made it impossible to discern the presence of point defects in the samples. Raman measurements demonstrated the presence of a particular mode that could be attributed to the formation of a 1:1 phase, the size of which is limited by requirements for charge compensation. The existence of an internal electric field between charged 1:1 nanoregions and the rest of material creates conditions for preferential positron annihilation that influence the obtained positron lifetime values. For BZN type materials it was found that the degree of 1:2 cation ordering decreases by increasing the sintering temperature to above 1400 °C.
Kinetics of the boron-oxygen related defect in theory and experiment
Authors: Herguth Axel , Hahn Giso
Published: December 2010

The formation of boron-oxygen complexes in boron-doped crystalline silicon can lead to a severe reduction in the minority charge carrier lifetime. This strongly influences, e.g., solar cell efficiencies if the material is used for photovoltaic application. Recent investigations have shown that a recovery of the carrier lifetime can be achieved by a subsequent thermally enhanced reaction induced by charge carriers. A model of the reaction dynamics of the boron-oxygen complex by means of rate equations is presented in this paper. Following a mathematical description of the reactions involved, the consequences based on the calculations are presented and allow a prediction of the observable electrical parameters. The fundamental agreement with measured data is proven experimentally for different phenomena.
Cross-plane phonon transport in thin films
Authors: Sellan D. P. , Turney J. E. , McGaughey A. J. H. , Amon C. H.
Published: December 2010

We predict the cross-plane phonon thermal conductivity of Stillinger-Weber silicon thin films as thin as 17.4 nm using the lattice Boltzmann method. The thin films are modeled using bulk phonon properties obtained from harmonic and anharmonic lattice dynamics calculations. We use this approach, which considers all of the phonons in the first Brillouin-zone, to assess the suitability of common assumptions. Specifically, we assess the validity of: (i) neglecting the contributions of optical modes, (ii) the isotropic approximation, (iii) assuming an averaged bulk mean-free path, and (iv) the Matthiessen rule. Because the frequency-dependent contributions to thermal conductivity change as the film thickness is reduced, assumptions that are valid for bulk are not necessarily valid for thin films.
Macroscopic quantum phenomena in Josephson structures
Authors: Barone A. , Lombardi F. , Rotoli G. , Tafuri F.
Published: December 2010

The Josephson effect is a probe with unparalleled capabilities for the study of a variety of macroscopic quantum phenomena. This is a survey of important achievements and challenging trends, in particular macroscopic quantum tunneling and energy level quantization. We focus on high-TC superconducting structures and recent research on nanostructures.
Low loss superconducting titanium nitride coplanar waveguide resonators
Authors: Vissers M. R. , Gao J. , Wisbey D. S. , Hite D. A. , Tsuei C. C. , Corcoles A. D. , Steffen M. , Pappas D. P.
Published: December 2010

Thin films of TiN were sputter-deposited onto Si and sapphire wafers with and without SiN buffer layers. The films were fabricated into rf coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in both the many photon and single photon limits, i.e., high and low electric field regimes, respectively. At high field, we found the highest internal quality factors (∼107) were measured for TiN with predominantly a (200)-TiN orientation. The (200)-TiN is favored for growth at high temperature on either bare Si or SiN buffer layers. However, growth on bare sapphire or Si(100) at low temperature resulted in primarily a (111)-TiN orientation. Ellipsometry and Auger measurements indicate that the (200)-TiN growth on the bare Si substrates is correlated with the formation of a thin, ≈2 nm, layer of SiN during the predeposition procedure. On these surfaces we found a significant increase of Qi for both high and low electric field regimes.
Lorentz force velocimetry based on time-of-flight measurements
Authors: Viré Axelle , Knaepen Bernard , Thess André
Published: December 2010

Lorentz force velocimetry (LFV) is a contactless technique for the measurement of liquid metal flowrates. It consists of measuring the force acting upon a magnetic system and arising from the interaction between an external magnetic field and the flow of an electrically conducting fluid. In this study, a new design is proposed so as to make the measurement independent of the fluid’s electrical conductivity. It is made of one or two coils placed around a circular pipe. The forces produced on each coil are recorded in time as the liquid metal flows through the pipe. It is highlighted that the auto- or cross-correlation of these forces can be used to determine the flowrate. The reliability of the flowmeter is first investigated with a synthetic velocity profile associated with a single vortex ring, which is convected at a constant speed. This configuration is similar to the movement of a solid rod and enables a simple analysis of the flowmeter. Then, the flowmeter is applied to a realistic three-dimensional turbulent flow. In both cases, the influence of the coil radii, coil separation, and sign of the coil-carrying currents is systematically assessed. The study is entirely numerical and uses a second-order finite volume method. Two sets of simulations are performed. First, the equations of motion are solved without accounting for the effect of the magnetic field on the flow (kinematic simulations). Second, the Lorentz force is explicitly added to the momentum balance (dynamic simulations), and the influence of the external magnetic field on the flow is then quantified.
Enhancement of ferromagnetic properties in Zn0.95Co0.05O nanoparticles by indium codoping: An experimental and theoretical study
Authors: Jayakumar O. D. , Sudakar C. , Persson C. , Salunke H. G. , Naik R. , Tyagi A. K.
Published: December 2010

Nanoparticles of Zn0.95−xCo0.05InxO (x=0.0 to 0.07) were synthesized by the pyrolitic reaction of sol-gels obtained from respective metal precursors. X-ray diffraction and high-resolution transmission electron microscopy studies confirm the formation of impurity-free wurtzite type ZnO structure for all the compositions. While pristine ZnO is diamagnetic, Zn0.95Co0.05O nanoparticles show weak paramagnetic behavior at room temperature. When “In.” is codoped with Co with x=0.0 to 0.07 in Zn0.95−xCo0.05InxO, a systematic increase in magnetic moment is observed up to x=0.07. First-principles modeling supports that the ferromagnetic phase become more favorable at higher indium doping concentrations.
A kinetics model for martensite variants rearrangement in ferromagnetic shape memory alloys
Authors: Wang Xingzhe , Li Fang
Published: December 2010

A kinetics model describing macroscopic behavior of martensitic variants rearrangement in ferromagnetic shape memory alloys is proposed. The model is based on a tensor description of thermodynamic continuum mechanics taking into account magnetomechanical coupling on the rearrangement process. A generalized thermodynamic driving force which rearranges the martensitic variants is derived. The thermodynamic evolution equations of the kinetics are obtained by means of the dissipation, which is induced by the twin boundary motion during rearrangement process, reaching a maximum. The ability of the model to characterize the macroscopic stress-strain behavior and magnetic field-induced strain of a ferromagnetic shape memory alloy rod under both magnetic field and stress field is demonstrated. The application of the theoretical kinetics model shows the good agreement with experimental observation.
Electro-optic and dielectric properties of optical switching devices based on liquid crystal dispersions and driven by conducting polymer [poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS)]-coated electrodes
Authors: Boussoualem Mourad , King Roch Chan Yu , Brun Jean-François , Duponchel Benoît , Ismaili Mimoun , Roussel Frédérick
Published: December 2010

We report on the electro-optic and dielectric properties of optical switching devices based on poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes sandwiching a polymer-dispersed liquid crystal (PDLC) layer. We demonstrate that the frequency dependence of the driving electric field on the optical properties of these devices allows the fabrication of flexible bandpass light modulators. The (PEDOT:PSS) electrodes are characterized using UV-Vis, scanning electron microscopy, Raman, conductive atomic force microscopy, and linear four probe technique. The PEDOT:PSS/PDLC-based displays exhibit similar electro-optical performances to those of ITO-based devices. In addition, it can function as a bandpass light modulator. This behavior resulted from depolarization fields (Maxwell–Wagner–Sillars effects) occurring (i) at the polymer/LC interface (low frequency) and (ii) between nanometer-sized conductive PEDOT-rich domains and poorly conductive PSS-rich areas present in the bulk and at the surface of the electrode (high frequency).