bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic force microscopy and Raman investigation on the sintering process of amorphous SiO2 nanoparticles
Authors: Buscarino G. , Ardizzone V. , Vaccaro G. , Agnello S. , Gelardi F. M.
Published: October 2010

We report an experimental investigation on the sintering process induced in fumed silica powders by isochronal thermal treatments at T=1270 K. Three types of fumed silica are considered, consisting of amorphous SiO2 (a-SiO2) particles with mean diameters 7, 14, and 40 nm. The study is performed by atomic force microscopy (AFM), to follow the morphological changes, and by Raman scattering, to obtain information on the concomitant structural modifications. The former method indicates that the sintering process proceeds by aggregation of single particles into larger grains, whose sizes increase with the thermal treatment duration. Furthermore, for each fumed silica type considered, the quantitative analysis of the AFM images shows that the grain growth process takes place approximately at constant rate for thermal treatment durations up to 290 h. Nevertheless, the value of the grain growth rate is sensitive to the system properties. In fact, it is found to increase with decreasing the particle mean diameter, giving a strong quantitative evidence of the size-dependence of the sintering process. On the other hand, Raman measurements indicate that the structure of the as-received fumed silica nanoparticles is significantly modified with respect to that of ordinary bulk a-SiO2, in agreement with previous experimental evidences. However, it rapidly relaxes upon thermal treatment at T=1270 K and its characterizing features are almost completely lost after treatment for about 80 h. Finally, the comparison of AFM and Raman data shows that the nanoparticles structure are completely relaxed (resembling that of bulk a-SiO2) when the grains formed by thermal treatment reach diameters greater than about 43 nm, indicating that it represents the characteristic size above which the effects of spatial confinement on the structure of the material become almost negligible.
Sulfoxide stretching mode as a structural reporter via dual-frequency two-dimensional infrared spectroscopy
Authors: Keating Christopher S. , McClure Beth A. , Rack Jeffrey J. , Rubtsov Igor V.
Published: October 2010

The SO stretching mode in sulfoxides, having a frequency in the 950–1150 cm−1 range, is tested as a structural label via dual-frequency two-dimensional infrared (2DIR) spectroscopy. The properties of this structural reporter are studied in several compounds, including (4,4′-dimethyl-2,2′-bipyridyl)(o-methylsulfinylbenzoate) ruthenium II, [Ru(dmb)2(BzSO)]+, (RuBzSO), octylsulfinylpropionic acid (OSPA), and o- and p-methylsulfinyl-benzoic acid (oMSBA and pMSBA). The mode assignment in the fingerprint region for these compounds is made using a combination of density functional theory calculations and 2DIR and relaxation-assisted 2DIR (RA 2DIR) spectroscopies. The SO stretching mode frequency and IR intensity demonstrate substantial sensitivity to the molecular structure. Multiple cross peaks of the CO and SO stretching modes with modes in the fingerprint region (930–1450 cm−1) were recorded. The 2DIR and RA 2DIR spectra focusing at interactions of a high-frequency mode of a ligand with the modes in the fingerprint region provide a spectral fingerprint of a compound and help mode assignment in the often congested fingerprint region. The cross-peak amplitudes in oMSBA, pMSBA, and OSPA were compared with the theoretical predictions based on the computed values for the off-diagonal anharmonicities and a reasonable match is found. The SO stretching mode provides means for assigning other modes in the fingerprint region and constitutes a promising structural reporter for the 2DIR and RA 2DIR spectroscopy measurements.
Heuristic optimization in penumbral image for high resolution reconstructed image
Authors: Azuma R. , Nozaki S. , Fujioka S. , Chen Y. W. , Namihira Y.
Published: October 2010

Penumbral imaging is a technique which uses the fact that spatial information can be recovered from the shadow or penumbra that an unknown source casts through a simple large circular aperture. The size of the penumbral image on the detector can be mathematically determined as its aperture size, object size, and magnification. Conventional reconstruction methods are very sensitive to noise. On the other hand, the heuristic reconstruction method is very tolerant of noise. However, the aperture size influences the accuracy and resolution of the reconstructed image. In this article, we propose the optimization of the aperture size for the neutron penumbral imaging.
Enhanced numerical analysis of current-voltage characteristics of long wavelength infrared n-on-p HgCdTe photodiodes
Authors: Jóźwikowski K. , Kopytko M. , Rogalski A. , Jóźwikowska A.
Published: October 2010

An enhanced original computer program is applied to explain in detail the current-voltage characteristics of n-on-p long wavelength infrared HgCdTe photodiodes. The computer program solves the system of nonlinear continuity equations for carriers and Poisson equations. In the model ideal diode diffusion, generation-recombination, band-to-band tunneling, trap-assisted tunneling, and impact ionization are included as potential limiting mechanisms in the photodiodes. It is a clearly explained influence of Hg-vacancy doping and extrinsic doping of an active device region on dark current-voltage characteristics and an R0A product of HgCdTe photodiodes in a wide region of temperature and wavelengths. Special attention is directed to the dependence of tunneling probability on the shape of potential barrier with in an depletion region. The theoretical predictions are compared with experimental data of high quantity photodiodes published in the available literature.
Effect of temperature on the electrical properties of an organic memristive device
Authors: Allodi Valentina , Erokhin Victor , Fontana M. P.
Published: October 2010

Electrical characterization of an organic memristive device shows an unexpected dependence of the conductivity variation with temperature, namely, slowing down of kinetics with increasing temperature. The observed behavior was explained by the hydration of the solid electrolyte layer, which is more significant at lower temperatures. It was possible to stabilize the device properties by protecting it with inert insulating material.
Laser generated neutron source for neutron resonance spectroscopy
Authors: Higginson D. P. , McNaney J. M. , Swift D. C. , Bartal T. , Hey D. S. , Kodama R. , Le Pape S. , Mackinnon A. , Mariscal D. , Nakamura H. , Nakanii N. , Tanaka K. A. , Beg F. N.
Published: October 2010

A neutron source for neutron resonance spectroscopy has been developed using high-intensity, short-pulse lasers. This technique will allow robust measurement of interior ion temperature of laser-shocked materials and provide insight into material equation of state. The neutron generation technique uses laser-accelerated protons to create neutrons in LiF through (p,n) reactions. The incident proton beam has been diagnosed using radiochromic film. This distribution is used as the input for a (p,n) neutron prediction code which is validated with experimentally measured neutron yields. The calculation infers a total fluence of 1.8×109 neutrons, which are expected to be sufficient for neutron resonance spectroscopy temperature measurements.
On the secondary flow through bifurcating pipes
Authors: Evegren Philip , Fuchs Laszlo , Revstedt Johan
Published: October 2010

The secondary motion induced by flow through curves and bifurcations has been subject to investigation over long time due to its importance in physiological and technological applications. In contrast to the flow in a straight pipe, curvature leads to the formation of secondary flow which is often unsteady. Streamline curvature occurs also in bifurcating pipes leading to some corresponding secondary, unsteady flow. This paper presents a detailed description of the unsteady flow in the daughter branch after a 90° bifurcation. A range of Reynolds and Womersley numbers are investigated. The results show the presence of Dean vortices and additional vortical patterns not reported in the literature. Both the streamwise (axial) and the secondary velocity components change character at larger Womersley numbers, leading to less complex secondary flow. Also, at larger Reynolds numbers, flow instabilities are observed. The secondary flow may lead to the formation of unsteady separation bubbles. This in turn yields peaks in the wall shear stress components. Such wall shear stress variations have often been related in the literature to the development process of atherosclerosis.
Insertion-induced breakage of materials
Authors: Yang Fuqian
Published: October 2010

Extensive experiments have shown the breakage of active materials, such as Sn and Si, after several charging and discharging in the development of rechargeable Li-ion batteries. To understand the breakage behavior due to the insertion and deinsertion of lithium into the active materials, the effect of surface mechanics and the insertion-induced deformation is examined within the theory of linear elasticity. An approach is presented whereby the average size of the fragment pieces due to the insertion of lithium into a spherical particle is governed by the equilibrium of the system energies before and after the breakage, in which the contribution of the insertion-induced deformation to both the total stored strain energy and the total surface energy is included in the calculation of free energy. The ratio of the average size of the fragment pieces to the radius of the spherical particle is relatively independent of the particle size in the range of millimeter to micrometer, and the ratio is a function of material properties and the volume expansion due to the lithium-insertion.
Diagnosing on plasma plume from xenon Hall thruster with collisional-radiative model
Authors: Yang Juan , Yokota Shigeru , Kaneko Ryotaro , Komurasaki Kimiya
Published: October 2010

The collisional-radiative model for xenon is used to calculate the electron density and temperature, and the atom population distribution in the plasma plume from a xenon Hall thruster. In the calculation, 173 levels of atom population are considered; only the processes of electron induced excitation and deexcitation, and spontaneous decay are simulated. The plasma plume is assumed to be optically thin. Consequently, the reasonable parameters of plasma plume along the outside center line of the thruster channel are obtained by making the calculated emission spectrum corresponding to measured ones and based on the atomic data available on site and by codes.
Structural anisotropy of nonpolar and semipolar InN epitaxial layers
Authors: Darakchieva V. , Xie M.-Y. , Franco N. , Giuliani F. , Nunes B. , Alves E. , Hsiao C. L. , Chen L. C. , Yamaguchi T. , Takagi Y. , Kawashima K. , Nanishi Y.
Published: October 2010

We present a detailed study of the structural characteristics of molecular beam epitaxy grown nonpolar InN films with a- and m-plane surface orientations on r-plane sapphire and (100) γ-LiAlO2, respectively, and semipolar (101¯1) InN grown on r-plane sapphire. The on-axis rocking curve (RC) widths were found to exhibit anisotropic dependence on the azimuth angle with minima at InN [0001] for the a-plane films, and maxima at InN [0001] for the m-plane and semipolar films. The different contributions to the RC broadening are analyzed and discussed. The finite size of the crystallites and extended defects are suggested to be the dominant factors determining the RC anisotropy in a-plane InN, while surface roughness and curvature could not play a major role. Furthermore, strategy to reduce the anisotropy and magnitude of the tilt and minimize defect densities in a-plane InN films is suggested. In contrast to the nonpolar films, the semipolar InN was found to contain two domains nucleating on zinc-blende InN(111)A and InN(111)B faces. These two wurtzite domains develop with different growth rates, which was suggested to be a consequence of their different polarity. Both, a- and m-plane InN films have basal stacking fault densities similar or even lower compared to nonpolar InN grown on free-standing GaN substrates, indicating good prospects of heteroepitaxy on foreign substrates for the growth of InN-based devices.
Density functional theory study of BN-doped graphene superlattice: Role of geometrical shape and size
Authors: Xu B. , Lu Y. H. , Feng Y. P. , Lin J. Y.
Published: October 2010

Effects of geometric shape and size of embedded boron nitride (BN) nanodot on the electronic and magnetic properties of the BN-doped graphene superlattices are systematically studied by spin-polarized first-principles calculations. The band gap of graphene superlattice is found to increase with the size of the BN nanodot, regardless of the shape of BN nanodot. Midgap states are found for graphene superlattices with triangular BN nanodots, and the number of such midgap states is determined by the imbalance between the number of carbon atoms occupying A- and B-sublattices, which is closely related to the geometric shape and size of the BN nanodot. When B and N atoms in the superlattices are exchanged, the valance bands and conduction bands are inverted with respect to the Fermi level due to electron-hole symmetry. Furthermore, partial occupation of the midgap states induces spin-polarization, and results in a magnetic ground state for the BN-doped graphene superlattices with triangular BN nanodots. Through electron or hole injection, the magnetic moment of the BN-doped graphene superlattice can be tuned, which may find applications in spintronic devices.
Quantitative scanning probe microscope topographies by charge linearization of the vertical actuator
Authors: Fleming Andrew J.
Published: October 2010

Many forms of scanning probe microscopy require a piezoelectric actuator to vary the probe-sample distance. Examples include constant-force atomic force microscopy and constant-current scanning tunneling microscopy. In such modes, the topography of the sample is reconstructed from the voltage applied to the vertical piezoelectric actuator. However, piezoelectric actuators exhibit significant hysteresis which can produce up to 14% uncertainty in the reproduced topography. In this work, a charge drive is used to linearize the vertical piezoelectric actuator which reduces the error from 14% to 0.65%.
Magnetization pinning at a Py/Co interface measured using broadband inductive magnetometry
Authors: Kennewell K. J. , Kostylev M. , Ross N. , Magaraggia R. , Stamps R. L. , Ali M. , Stashkevich A. A. , Greig D. , Hickey B. J.
Published: October 2010

Broadband ferromagnetic resonance responses for metallic single-layer and bilayer magnetic films with total thicknesses smaller than the microwave magnetic skin depth have been studied. Two different types of microwave stripline transducers were used to excite and detect magnetization precession: a coplanar waveguide and a microstrip line both with characteristic width larger than the free propagation path for traveling spin waves along the film. Both transducers show efficient excitation of higher-order standing spin wave modes across the film thickness in samples 30–91 nm thick. The ratio of amplitudes of the first standing spin wave to the fundamental resonant mode is independent of frequency for single-layer permalloy films. In contrast, we find a strong variation in the amplitudes with frequency for cobalt–Permalloy bilayers and the ratio is strongly dependent on the ordering of layers with respect to a stripline transducer. Most importantly, cavity ferromagnetic resonance measurements on the same samples show considerably weaker amplitudes for the standing spin waves. All experimental data are consistent with expected effects of eddy currents in films with thicknesses below the microwave magnetic skin depth. Finally, conditions for observing eddy current effects in different types of experiments are critically examined.
Communication: Second-order multireference perturbation theory with explicit correlation: CASPT2-F12
Authors: Shiozaki Toru , Werner Hans-Joachim
Published: October 2010

An explicitly correlated complete active space second-order perturbation (CASPT2-F12) method is presented which strongly accelerates the convergence of CASPT2 energies and properties with respect to the basis set size. A Slater-type geminal function is employed as a correlation factor to represent the electron-electron cusp of the wave function. The explicitly correlated terms in the wave function are internally contracted. The required density matrix elements and coupling coefficients are the same as in conventional CASPT2, and the additional computational effort for the F12 correction is small. The CASPT2-F12 method is applied to the singlet-triplet splitting of methylene, the dissociation energy of ozone, and low-lying excited states of pyrrole.
Floating potential of a small particle in a plasma: Difference between Maxwellian and Druyvesteyn electron velocity distributions
Authors: Khrapak Sergey
Published: October 2010

The floating potential of a small spherical particle immersed in a plasma is calculated for two different electron velocity distributions functions, Maxwellian and Druyvesteyn ones. It is shown that for plasma conditions typical for laboratory gas discharges, the difference between the floating potentials for these two distributions is small, provided the mean energy of the electrons is the same. The obtained results can be useful in the context of complex (dusty) plasmas.
Preferential concentration of heavy particles: A Voronoï analysis
Authors: Monchaux R. , Bourgoin M. , Cartellier A.
Published: October 2010

We present an experimental characterization of preferential concentration and clustering of inertial particles in a turbulent flow obtained from Voronoï diagram analysis. Several results formerly obtained from various data processing techniques are successfully recovered and further analyzed with Voronoï tesselations as the main single tool. We introduce a simple and nonambiguous way to identify particle clusters. We emphasize the maximum preferential concentration for particles with Stokes numbers around unity and the self-similar nature of clustering and we report new unpredicted results concerning clusters inner concentration dependence on Stokes number and global seeding density. Some of these experimental observations can be consistently interpreted in the context of the so-called sweep-stick mechanism. Finally, we stress the great potential of Voronoï analysis that offers important openings for new investigations of particle laden flows in terms, for instance, of simultaneous Lagrangian statistics of particle dynamics and local concentration field.
Thermal conduction in thin films measured by optical surface thermal lensing
Authors: Bourgoin Jean-Philippe , Allogho Guy-Germain , Haché Alain
Published: October 2010

Thermal conduction across thin films is measured optically by using the surface thermal lensing effect. Pump-probe laser measurements combined with numerical modeling are used to study thermal conduction in a variety of materials as thin as 10 nm. The method is relatively simple, robust, rapid, and offers an alternative to current techniques. Thermal conductivity in gold films is found to drop from 300 to 100 W/Km when the film thickness is reduced from 2000 to 100 nm. Results for silver, tin and aluminum films are also presented and compared with results from other studies.
Magnetism and magnetotransport of strongly disordered Zn1−xMnxGeAs2 semiconductor: The role of nanoscale magnetic clusters
Authors: Kilanski L. , Górska M. , Dobrowolski W. , Dynowska E. , Wójcik M. , Kowalski B. J. , Anderson J. R. , Rotundu C. R. , Maude D. K. , Varnavskiy S. A. , Fedorchenko I. V. , Marenkin S. F.
Published: October 2010

We present systematic studies of magnetic and transport properties of Zn1−xMnxGeAs2 semimagnetic semiconductor with the chemical composition varying between 0.053≤x≤0.182. The transport characterization showed that all investigated samples had p-type conductivity strongly depending on the chemical composition of the alloy. The Hall effect measurements revealed carrier concentrations p≥1019 cm−3 and relatively low mobilities, μ≤15 cm2/(V s), also chemical composition dependent. The magnetic investigations showed the presence of paramagnet-ferromagnet phase transitions with transition temperatures greater than 300 K for the samples with x≥0.078. We prove by means of x-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy techniques that the observed room temperature ferromagnetism is due to the presence of MnAs inclusions. The high field magnetoresistance showed the presence of giant magnetoresistance effect with maximum amplitudes around 50% due to the presence of nanosize ferromagnetic grains.
Optical, structural, and chemical properties of flash evaporated In2S3 buffer layer for Cu(In,Ga)Se2 solar cells
Authors: Verma Rajneesh , Datta Debjit , Chirila Adrian , Güttler Dominik , Perrenoud Julian , Pianezzi Fabian , Müller Ulrich , Kumar Satyendra , Tiwari Ayodhya N.
Published: October 2010

In 2 S 3 layers were deposited by flash evaporation technique with varying flash rates. The optical constants of layers based on Tauc–Lorentz model dielectric function were extracted from spectroscopic ellipsometry measurements. X-ray photoelectron spectroscopic investigation revealed the presence of oxygen impurity in as-deposited and air-annealed layers with traces of Na inclusion in the layer grown at high flash rate. The enhancement in crystalline arrangement of as-deposited layer after air annealing was confirmed by Raman spectroscopy. Rutherford backscattering measurements revealed the growth of off-stoichiometric layers at all flash rates. An analytical layer growth model has been proposed supporting the results obtained by various layer characterization techniques. The solar cells were prepared with flash evaporated In2S3 buffer layers and their performances were compared with CdS reference solar cell. A significant gain in short-circuit current was obtained after air annealing of the complete device at 200 °C for 20 min. A maximum conversion efficiency of 12.6% was delivered by a high flash rate In2S3 buffered cell with open-circuit voltage close to that of CdS reference cell. The improvement in device performance after air annealing treatment is explained by thermally enhanced Cu and oxygen diffusion from Cu(In,Ga)Se2 and i-ZnO to In2S3 layer, respectively.
Basis set representation of the electron density at an atomic nucleus
Authors: Mastalerz Remigius , Widmark Per-Olof , Roos Björn Olof , Lindh Roland , Reiher Markus
Published: October 2010

In this paper a detailed investigation of the basis set convergence for the calculation of relativistic electron densities at the position of finite-sized atomic nuclei is presented. The development of Gauss-type basis sets for such electron densities is reported and the effect of different contraction schemes is studied. Results are then presented for picture-change corrected calculations based on the Douglas–Kroll–Hess Hamiltonian. Moreover, the role of electron correlation, the effect of the numerical integration accuracy in density functional calculations, and the convergence with respect to the order of the Douglas–Kroll–Hess Hamiltonian and the picture-change-transformed property operator are studied.
Transition levels of defect centers in ZnO by hybrid functionals and localized basis set approach
Authors: Gallino Federico , Pacchioni Gianfranco , Di Valentin Cristiana
Published: October 2010

A hybrid density functional study based on a periodic approach with localized atomic orbital basis functions has been performed in order to compute the optical and thermodynamic transition levels between different charge states of defect impurities in bulk ZnO. The theoretical approach presented allows the accurate computation of transition levels starting from single particle Kohn–Sham eigenvalues. The results are compared to previous theoretical findings and with available experimental data for a variety of defects ranging from oxygen vacancies, zinc interstitials, and hydrogen and nitrogen impurities. We find that H and Zn impurities give rise to shallow levels; the oxygen vacancy is stable only in the neutral VO and doubly charged VO2+ variants, while N-dopants act as deep acceptor levels.
High-pressure x-ray diffraction study of bulk and nanocrystalline PbMoO4
Authors: Errandonea D. , Santamaria-Perez D. , Grover V. , Achary S. N. , Tyagi A. K.
Published: October 2010

We studied the effects of high-pressure on the crystalline structure of bulk and nanocrystalline scheelite-type PbMoO4. We found that in both cases the compressibility of the materials is highly nonisotropic, being the c-axis the most compressible one. We also observed that the volume compressibility of nanocrystals becomes higher that the bulk one at 5 GPa. In addition, at 10.7(8) GPa we observed the onset of an structural phase transition in bulk PbMoO4. The high-pressure phase has a monoclinic structure similar to M-fergusonite. The transition is reversible and not volume change is detected between the low-pressure and high-pressure phases. No additional structural changes or evidence of decomposition are found up to 21.1 GPa. In contrast nanocrystalline PbMoO4 remains in the scheelite structure at least up to 16.1 GPa. Finally, the equation of state for bulk and nanocrystalline PbMoO4 are also determined.
Photonic crystals with defect structures fabricated through a combination of holographic lithography and two-photon lithography
Authors: Ohlinger Kris , Torres Faraon , Lin Yuankun , Lozano Karen , Xu Di , Chen Kevin P.
Published: October 2010

This paper presents the capability of direct laser writing of complex defect structures in holographically formed three-dimensional photonic crystals in dipentaerythritol penta/hexaacrylate (DPHPA) monomers mixed with photoinitiators. The three-dimensional photonic crystal template was fabricated through prism-based holographic lithography. Defect structures are fabricated through the two-photon polymerization excited by a femtosecond laser. The strengths of two optical lithographic techniques are combined with holographic lithography providing a rapid and large area microfabrication and two-photon lithography providing flexibility in fabrication of defect structures. The optical fabrication process is simplified in the negative tone DPHPA without prebake and postexposure bake as is required of SU-8 while maintaining a capability for constructing photonic structures with small features.
Water distributions in polystyrene-block-poly[styrene-g-poly(ethylene oxide)] block grafted copolymer system in aqueous solutions revealed by contrast variation small angle neutron scattering study
Authors: Li Xin , Hong Kunlun , Liu Yun , Shew Chwen-Yang , Liu Emily , Herwig Kenneth W. , Smith Gregory S. , Zhao Junpeng , Zhang Guangzhao , Pispas Stergios , Chen Wei-Ren
Published: October 2010

We develop an experimental approach to analyze the water distribution around a core-shell micelle formed by polystyrene-block-poly[styrene-g-poly(ethylene oxide (PEO)] block copolymers in aqueous media at a fixed polymeric concentration of 10 mg/ml through contrast variation small angle neutron scattering (SANS) study. Through varying the D2O/H2O ratio, the scattering contributions from the water molecules and the micellar constituent components can be determined. Based on the commonly used core-shell model, a theoretical coherent scattering cross section incorporating the effect of water penetration is developed and used to analyze the SANS I(Q). We have successfully quantified the intramicellar water distribution and found that the overall micellar hydration level increases with the increase in the molecular weight of hydrophilic PEO side chains. Our work presents a practical experimental means for evaluating the intramacromolecular solvent distributions of general soft matter systems.
Reduction of polymer surface tension by crystallized polymer nanoparticles
Authors: Thompson Russell B. , Park Chul B. , Chen P.
Published: October 2010

Self-consistent field theory is applied to investigate the effects of crystallized polymer nanoparticles on polymer surface tension. It is predicted that the nanoparticles locate preferentially at the polymer surface and significantly reduce the surface tension, in agreement with experiment. In addition to the reduction of surface tension, the width of the polymer surface is found to narrow. The reduced width and surface tension are due to the smaller spatial extent of the nanoparticles compared to the polymer. This allows the interface to become less diffuse and so reduces the energies of interaction at the surface, which lowers the surface tension. The solubility of the surrounding solvent phase into the polymer melt is mostly unchanged, a very slight decrease being detectable. The solubility is constant because away from the interface, the system is homogeneous and the replacement of polymer with nanoparticles has little effect.
A semilinear wave equation with space-time dependent coefficients and a memory boundarylike antiperiodic condition: Regularity and stability
Authors: Lê Út V.
Published: October 2010

This paper deals with regularity and stability of solutions to an initial-boundary value problem of a semilinear wave equation. This equation admits space-time dependent coefficients and a memory boundarylike antiperiodic condition. For regularity or existence of a unique strong solution, the Faedo–Galerkin method and the energy method, associated with the maximal solution of a nonlinear Volterra integral equation, are applied. Then, as an application of the regularity result, stability of this unique strong solution is obtained by the energy method.
A fixed point method for perturbation of bimultipliers and Jordan bimultipliers in C∗-ternary algebras
Authors: Ebadian A. , Ghobadipour N. , Eshaghi Gordji M.
Published: October 2010

Let A be a C∗-ternary algebra. A C-bilinear T:A×A→A is called a C∗-ternary algebra bi-multiplier, if it satisfies T([abc],d)=[T(a,b)cd], T(a,[bcd])=[abT(c,d)] for all a,b,c,d∊A. Also, the mapping T:A×A→A is a called C∗-ternary algebra Jordan bimultiplier, if it satisfies T([aaa],a)=[T(a,a)aa], T(a,[aaa])=[aaT(a,a)] for all a∊A. Using the fixed point method, we investigate the generalized Hyers–Ulam–Rassias stability of bimultipliers and Jordan bimultipliers in C∗-ternary algebras. The concept of Hyers–Ulam–Rassias stability originated from the Th.M. Rassias’ stability theorem that appeared in his paper: [Th. M. Rassias, Proc. Am. Math. Soc. 72, 297 (1978)].
Conducting interfaces between band insulating oxides: The LaGaO3/SrTiO3 heterostructure
Authors: Perna P. , Maccariello D. , Radovic M. , Scotti di Uccio U. , Pallecchi I. , Codda M. , Marré D. , Cantoni C. , Gazquez J. , Varela M. , Pennycook S. J. , Granozio F. Miletto
Published: October 2010

We show that the growth of the heterostructure LaGaO3/SrTiO3 yields the formation of a highly conductive interface. Our samples were carefully analyzed by high resolution electron microscopy, in order to assess their crystal perfection and to evaluate the abruptness of the interface. Their carrier density and sheet resistance are compared to the case of LaAlO3/SrTiO3 and a superconducting transition is found. The results open the route to widening the field of polar-nonpolar interfaces, pose some phenomenological constrains to their underlying physics and highlight the chance of tailoring their properties for future applications by adopting suitable polar materials.
Water adsorption isotherms on porous onionlike carbonaceous particles. Simulations with the grand canonical Monte Carlo method
Authors: Hantal György , Picaud Sylvain , Hoang Paul N. M. , Voloshin Vladimir P. , Medvedev Nikolai N. , Jedlovszky Pál
Published: October 2010

The grand canonical Monte Carlo method is used to simulate the adsorption isotherms of water molecules on different types of model soot particles. These soot models are constructed by first removing atoms from onion-fullerene structures in order to create randomly distributed pores inside the soot, and then performing molecular dynamics simulations, based on the reactive adaptive intermolecular reactive empirical bond order (AIREBO) description of the interaction between carbon atoms, to optimize the resulting structures. The obtained results clearly show that the main driving force of water adsorption on soot is the possibility of the formation of new water-water hydrogen bonds with the already adsorbed water molecules. The shape of the calculated water adsorption isotherms at 298 K strongly depends on the possible confinement of the water molecules in pores of the carbonaceous structure. We found that there are two important factors influencing the adsorption ability of soot. The first of these factors, dominating at low pressures, is the ability of the soot of accommodating the first adsorbed water molecules at strongly hydrophilic sites. The second factor concerns the size and shape of the pores, which should be such that the hydrogen bonding network of the water molecules filling them should be optimal. This second factor determines the adsorption properties at higher pressures.
Middle-ultraviolet laser photoelectron emission from vertically aligned millimeter-long multiwalled carbon nanotubes
Authors: Yaghoobi Parham , Michan Mario , Nojeh Alireza
Published: October 2010

We demonstrate photoelectron emission from millimeter-long forests of vertically aligned multiwalled carbon nanotubes using 266 nm light, which illuminates the forests from the side. We have measured quantum efficiencies in the order of ∼10−5 at low fields (pure photoemission) and ∼10−3 at an applied field of 0.3 V μm−1, which are 2–4 orders of magnitude higher than those obtained from films of randomly oriented nanotubes, and approach the quantum efficiency of semimetal photocathodes. Through optical simulations we show that 266 nm light is absorbed within the first few layers of the nanotube forest.
Low damping resonant magnetoelectric sensors
Authors: Greve Henry , Woltermann Eric , Jahns Robert , Marauska Stephan , Wagner Bernhard , Knöchel Reinhard , Wuttig Manfred , Quandt Eckhard
Published: October 2010

The signal of magnetic sensors based on resonant cantilevers comprised of elastically coupled piezoelectric and magnetostrictive materials increases as the damping decreases. Here, we demonstrate that air damping which normally is suppressed by evacuation can also be substantially reduced by lowering the resonance frequency. We show that a Si-cantilever structured to include a seismic mass features a resonant magnetoelectric coupling coefficient of 1.8 kV/cmOe at 330 Hz in air.
An empirical potential for silicon under conditions of strong electronic excitation
Authors: Shokeen Lalit , Schelling Patrick K.
Published: October 2010

We present an empirical potential developed for silicon under conditions of strong electronic excitation. We show the essentially athermal nature of the melting transition when the electronic temperature is extremely high. The resulting liquid is shown to be distinct from ordinary liquid silicon. For less intense excitations, we determine the thermal melting temperature and demonstrate the possible existence of a regime where ordinary thermodynamic melting can occur but at a reduced temperature Tm. We show laser-induced softening of the lattice can lead to lattice cooling for very short time scales (∼100 fs), an effect never before recognized.
Dynamical revivals in spatiotemporal evolution of driven one dimensional box
Authors: Abbas Tasawar , Saif Farhan
Published: October 2010

We study periodically driven one dimensional box in the presence of weak modulating force and provide analytical calculations for time of quantum revivals and explain via spatiotemporal behavior. Presently introduced analysis can be applied to calculate the time of revivals in the system subject to any periodically changing weak external driving force. Spatiotemporal behavior provides the modified numerical values of revival times which have good agreement with our analytical results. Moreover, spatiotemporal evolution shows absence of symmetry beyond a revival time, which contributes to change of slope in subsequent canals and ridges.
Impact of Al content on transport properties of two-dimensional electron gas in GaN/AlxGa1−xN/GaN heterostructures
Authors: Polyakov V. M. , Cimalla V. , Lebedev V. , Köhler K. , Müller S. , Waltereit P. , Ambacher O.
Published: October 2010

The influence of the Al content on the mobility of the two-dimensional electron gas (2DEG) in GaN/AlxGa1−xN/GaN heterostructures is studied by employing the ensemble Monte Carlo method. Using two interface polarization charge models, we calculate the room temperature low-field mobility at different Al compositions of the barrier layer ranging from 8% up to 35%. All relevant scattering mechanisms are considered to provide a quantitative description of the measured mobilities. We show that 2DEG transport in the heterostructures is mostly affected by dislocation scattering for all Al contents examined. The role of alloy scattering and interface roughness scattering is also discussed.
Parylene-C passivated carbon nanotube flexible transistors
Authors: Selvarasah Selvapraba , Li Xinghui , Busnaina Ahmed , Dokmeci Mehmet R.
Published: October 2010

Carbon nanotubes are extremely sensitive to the molecular species in the environment and hence require a proper passivation technique to isolate them against environmental variations for the realization of reliable nanoelectronic devices. In this paper, we demonstrate a parylene-C passivation approach for CNT thin film transistors fabricated on a flexible substrate. The CNT transistors are encapsulated with 1 and 3 μm thick parylene-C coatings, and the transistor characteristics are investigated before and after passivation. Our findings indicate that thin parylene-C films can be utilized as passivation layers for CNT transistors and this versatile technique can be readily applied for the encapsulation of CNT devices such as field effect transistors, p-n diodes, and logic circuits fabricated on flexible substrates.
Coexistence of strong ferromagnetism and polar switching at room temperature in Fe3O4–BiFeO3 nanocomposite thin films
Authors: Weal E. , Patnaik S. , Bi Z. , Wang H. , Fix T. , Kursumovic A. , Driscoll J. L. MacManus
Published: October 2010

10% Fe3O4–90% BiFeO3 nanocomposite thin films of 180 nm thickness were grown by pulsed laser deposition on SrTiO3 (011) single crystals. A 3–4 nm nanolamella structure of Fe3O4 and BiFeO3 was formed. While BiFeO3 has the expected epitaxial relationship with the substrate, Fe3O4 grew epitaxially and highly strained (7%). Compared to pure Fe3O4 films of similar thickness, the nanolamella structure of Fe3O4 gives rise to a greatly enhanced saturation magnetization of 900 emu/cc, and, after field cooling, an enhanced coercivity of 450 Oe. Piezoresponse force microscopy measurements show similar polar switching properties between the nanocomposite and pure BiFeO3 films.
Electronic transitions and hybrid resonance in InAsSb films by reflectance spectra
Authors: Deng H. Y. , Wang Q. W. , He J. Y. , Sun C. H. , Hu S. H. , Chen X. , Dai N.
Published: October 2010

Electronic properties of InAs1−xSbx films with x up to 0.09 have been investigated by reflectance spectra in 1.5–5 eV energy range at room temperature. The real and imaginary parts of the dielectric function were derived by Kramers–Kronig analysis on the reflectance spectra, which show satisfactory agreement with the spectroscopic ellipsometry data. The E1′ and E1′+Δ1′ peaks are attributed to electronic interband transitions at the E1 and E1+Δ1 critical points, respectively. The prominent E2′ peaks, which exhibit high reflectivity and large blueshift, are found to be contributed by hybrid resonance due to the cooperative behavior of both E2-state electrons and plasmons.
Synchrotron vacuum ultraviolet radiation studies of the D Π1u state of H2
Authors: Dickenson G. D. , Ivanov T. I. , Roudjane M. , de Oliveira N. , Joyeux D. , Nahon L. , Tchang-Brillet W.-Ü. L. , Glass-Maujean M. , Haar I. , Ehresmann A. , Ubachs W.
Published: October 2010

The 3pπD Π1u state of the H2 molecule was reinvestigated with different techniques at two synchrotron installations. The Fourier transform spectrometer in the vacuum ultraviolet wavelength range of the DESIRS beamline at the SOLEIL synchrotron was used for recording absorption spectra of the D Π1u state at high resolution and high absolute accuracy, limited only by the Doppler contribution at 100 K. From these measurements, line positions were extracted, in particular, for the narrow resonances involving Π1u− states, with an accuracy estimated at 0.06 cm−1. The new data also closely match multichannel quantum defect calculations performed for the Π− components observed via the narrow Q-lines. The Λ-doubling in the D Π1u state was determined up to v=17. The 10 m normal incidence scanning monochromator at the beamline U125/2 of the BESSY II synchrotron, combined with a home-built target chamber and equipped with a variety of detectors, was used to unravel information on ionization, dissociation, and intramolecular fluorescence decay for the D Π1u vibrational series. The combined results yield accurate information on the characteristic Beutler–Fano profiles associated with the strongly predissociated Πu+ parity components of the D Π1u levels. Values for the parameters describing the predissociation width as well as the Fano-q line shape parameters for the J=1 and J=2 rotational states were determined for the sequence of vibrational quantum numbers up to v=17.
Thermotropic nematic and smectic order in silica glass nanochannels
Authors: Kityk Andriy V. , Huber Patrick
Published: October 2010

Optical birefringence measurements on a rodlike liquid crystal, octyloxycyanobiphenyl, imbibed in silica channels (7 nm diameter), are presented and compared to the thermotropic bulk behavior. The orientational and positional order of the confined liquid evolves continuously at the paranematic-to-nematic and sizeably broadened at the nematic-to-smectic order transition, respectively, in contrast to the discontinuous and well-defined second-order character of the bulk transitions. A Landau–de Gennes analysis reveals identical strengths of the nematic and smectic ordering fields (imposed by the walls) and indicates that the smectic order is more affected by quenched disorder (originating in channel tortuosity and roughness) than the nematic transition.
Excited states of the free excitons in CuInSe2 single crystals
Authors: Yakushev M. V. , Luckert F. , Faugeras C. , Karotki A. V. , Mudryi A. V. , Martin R. W.
Published: October 2010

High-quality CuInSe2 single crystals were studied using polarization resolved photoluminescence (PL) and magnetophotoluminescence (MPL). The emission lines related to the first (n=2) excited states for the A and B free excitons were observed in the PL and MPL spectra at 1.0481 meV and 1.0516 meV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 meV and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (EgA=1.050 eV and EgB=1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.
Near bulk semiconductor to metal transition in epitaxial VO2 thin films
Authors: Gupta Alok , Narayan Jagdish , Dutta Titas
Published: October 2010

We have been able to achieve semiconductor-to-metal transition (SMT) temperature in VO2 thin films close to the values reported for bulk VO2 single crystals. This was achieved by complete relaxation of misfit strain, which leads to a negligible tension/compression along VO2 [001], upon introduction of NiO buffer layer on c-plane sapphire substrate. In this paper, we discuss the mechanism behind complete relaxation of misfit strain which occurs under the paradigm of domain-matching epitaxy, where integral multiples of planes match across the interface. NiO buffer layers were grown in situ, prior to the VO2 deposition, using pulsed-laser deposition technique. X-ray θ-2θ, φ, and pole figure scans were performed for structural characterization of the VO2/NiO/Al2O3 (0001) heterostructure. All the constituent layers of the heterostructure were found to be epitaxial with orientation relationship: (020)VO2∥(111)NiO∥(0001)Al2O3 and ⟨100⟩VO2∥⟨110⟩NiO∥⟨101¯0⟩Al2O3. Parameters related to SMT, such as hysteresis and transition width were extracted from the Gaussian fit of temperature dependence of electrical resistance. These parameters have also been discussed in correlation with the strain along c-axis of VO2, in-plane orientation, and microstructure. A comparison has been made between the VO2 thin films deposited with and without NiO buffer layer on c-sapphire substrates to delineate the importance of strain relaxation in attaining near bulk SMT temperature values.
A Perception–Action Strategy for Hummingbirds
Authors: Delafield-Butt Jonathan , Galler Andreas , Schögler Benjaman , Lee David N
Published: October 2010

Many human and animal tasks are thought to be controlled with the τ informational variable. It is widely accepted that controlling the rate of change of τ (tau) during decelerative tasks, such as when braking or landing, is one common perceptual control strategy. However, many tasks require accelerating before decelerating to a goal, such as reaching. An advancement of τ theory shows how a single action formula may be used to control the full action unit from initiation to peak velocity, and to rest at the goal, with the same perceptual τ information as before and accounting for the same decelerative kinematics as before. Here, we test the theory against data from high-speed video of a hummingbird flying to its flower feeder. We find that the theory accounts for 97% of the variance in the data, and thus supports it.
The Importance of Laughing in Your Face: Influences of Visual Laughter on Auditory Laughter Perception
Authors: Jordan Timothy R , Abedipour Lily
Published: October 2010

Hearing the sound of laughter is important for social communication, but processes contributing to the audibility of laughter remain to be determined. Production of laughter resembles production of speech in that both involve visible facial movements accompanying socially significant auditory signals. However, while it is known that speech is more audible when the facial movements producing the speech sound can be seen, similar visual enhancement of the audibility of laughter remains unknown. To address this issue, spontaneously occurring laughter was edited to produce stimuli comprising visual laughter, auditory laughter, visual and auditory laughter combined, and no laughter at all (either visual or auditory), all presented in four levels of background noise. Visual laughter and no-laughter stimuli produced very few reports of auditory laughter. However, visual laughter consistently made auditory laughter more audible, compared to the same auditory signal presented without visual laughter, resembling findings reported previously for speech.
The Distance to NGC 5128 (Centaurus A)
Authors: Harris Gretchen L. H. , Rejkuba Marina , Harris William E.
Published: October 2010

In this paper we review the various high precision methods that are now available to determine the distance to NGC 5128. These methods include: Cepheids, TRGB (tip of the red giant branch), PNLF (planetary nebula luminosity function), SBF (surface brightness fluctuations), and Long Period Variable (LPV) Mira stars. From an evaluation of these methods and their uncertainties, we derive a best-estimate distance of 3.8±0.1 Mpc to NGC 5128 and find that this mean is now well supported by the current data. We also discuss the role of NGC 5128 more generally for the extragalactic distance scale as a testbed for the most direct possible comparison among these key methods.