bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigations of atomic structure and bonding at domain boundaries in bulk La0.5Eu0.2Sr0.3MnO3
Authors: Sun B. Z. , He L. L. , Luo F. , Yan C. H.
Published: July 2005

Perovskite ceramic samples of bulk La0.7Sr0.3MnO3 doped with Eu are prepared by usual thermal decomposition and grinding procedure. Besides La0.7Sr0.3MnO3 rhombohedral phase, with the substitution of Eu3+ for La3+, another perovskite‐based structure with orthorhombic symmetry and space group Pnma can be identified by means of electron diffraction patterns (EDP) and energy‐dispersive X‐ray spectroscopy (EDX). Many 120° large‐angle orientation domains with a three‐fold rotational symmetry relationship are observed in the orthorhombic grain. According to group theory of phase transformation and matrix analyses, the 120° orientation domain originates from the three‐fold symmetry axis of pseudo‐cubic parent phase. Meanwhile, a projected model of the domain boundary is constructed based on their orientation relationships. The distortions and arrangements of MnO6 octahedra on the domain boundary are discussed particularly. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of erbium–oxygen nanoclusters in erbium‐doped oxidized amorphous silicon
Authors: Bresler Mikhail , Gusev Oleg , Terukov Evgenii , Undalov Yurii
Published: July 2005

A “phase transition” model is presented, which treats quantitatively the experimental results obtained on erbium‐doped oxidized amorphous silicon. The model is based on the assumption that on the change of molar concentration of oxygen in the gaseous plasma during the preparation of erbium‐doped amorphous silicon at special oxygen concentrations supramolecular erbium–oxygen complexes (“clusters') are formed in the plasma, which are eventually deposited as separate species on the substrate. The threshold formation of such clusters is evidenced in the concentration of oxygen, oxygen–silicon bonds, silicon, and erbium in the erbium‐doped oxidized amorphous silicon film. Erbium photoluminescence is strongly enhanced due to the formation of large erbium–oxygen clusters, which can be regarded as erbium containing nanodielectric particles inserted in the semiconductor matrix and reveal advantages characteristic of erbium‐doped silicon dioxide with silicon nanocrystals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum fluid effects and parametric instabilities in microcavities
Authors: Ciuti Cristiano , Carusotto Iacopo
Published: July 2005

We present a description of the non‐equilibrium properties of a microcavity polariton fluid, injected by a nearly‐resonant continuous wave pump laser. In the first part, we point out the interplay between the peculiar dispersion of the Bogoliubov‐like polariton excitations and the onset of polariton parametric instabilities. We show how collective excitation spectra having no counterpart in equilibrium systems can be observed by tuning the excitation angle and frequency. In the second part, we explain the impact of these collective excitations on the in‐plane propagation of the polariton fluid. We show that the resonant Rayleigh scattering induced by artificial or natural defects is a very sensitive tool to reveal novel fascinating effects such as polariton superfluidity or to show new aspects of the Cherenkov effect. We present a comprehensive set of predicted far‐field and near‐field images for the resonant Rayleigh scattering emission. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bose–Einstein condensation of microcavity polaritons
Authors: Savona Vincenzo , Sarchi Davide
Published: July 2005

After resuming the basic facts about Bose–Einstein condensation of weakly interacting systems, we review the main experimental and theoretical works aimed at the realization of this intriguing phenomenon in the system of microcavity polaritons. All the experimental results until present suggest that Bose–Einstein condensation is still eluding the experimentalists' efforts. On the theoretical side, only recently polaritons have been described within a quantum field theory of an interacting Bose gas, suggesting that polariton condensation might occur at least as a consequence of polariton parametric scattering under resonant excitation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Chirality Factors and Their Application to QSAR Studies of Chiral Molecules
Authors: Yang Chunsheng , Zhong Chongli
Published: July 2005

Two series of chirality factors that can distinguish enantiomers and diastereomers were developed in this work and the corresponding chiral topological indices were proposed. The obtained chiral topological indices can be used to perform QSAR studies for chiral molecules. The biological activities of fourteen 3‐(3‐hydroxyphenyl)‐ piperidines (seven pairs of enantiomers), the high‐pressure thin‐layer chromatographic retention indices of eight hydroxy acids and ten amino acids (nine pairs of enantiomers), the ED50 of 23 ecdysteroids (19 pairs of diastereomers), and the corticosteroid‐binding globulins affinities of 31 steroids were used to evaluate the chirality factors and the corresponding chiral topological indices. The QSAR models developed give satisfactory predictive accuracy. Compared with the existing methods, the chirality factor method proposed in this work has the advantage of being applicable to the existing topological indices directly. This makes good use of the existing topological indices, and thus brings convenience to the QSAR studies for chiral molecules. Another advantage of the new method is that it can also correctly describe the characteristics of meso compounds.
Use of Topological Indices of Organic Sulfur Compounds in Quantitative Structure‐Retention Relationship Study
Authors: Safa F. , Hadjmohammadi M. R.
Published: July 2005

Structure‐gas chromatographic retention index models were developed for some organic sulfur compounds at four different temperatures (60, 80, 100 and 120 °C) using only topological descriptors. At first, regression models were generated for each temperature separately with high values of multiple correlation coefficient and Fisher‐ratio statistics. The results of cross validation test using leave‐one‐out (Q2≥0.956) and leave‐two‐out (Q2≥0.953) methods showed good predictive ability of the models developed. Then, a single combined quantitative structure‐retention relationship model, added temperature as a parameter, was also developed for all the temperatures, showing good statistical parameters (R=0.991 and F=728.474). The stability and validity of the combined model were verified by both internal (Q2>0.970) and external validation (Q$\rm{ {_{prediction\;set}^{2}}}$=0.993) techniques. The results of the study indicated the efficiency of the classical topological descriptors in simultaneous prediction of retention index values of sulfur compounds at different temperatures. The topological descriptors well covered the molecular properties known to be relevant for gas chromatographic retention data, such as molecular size and degree of branching.
Symbolic methods for invariant manifolds in chemical kinetics
Authors: Fraser Simon J.
Published: July 2005

Chemical reactions show a separation of time scales in transient decay due to the stiffness of the ordinary differential equations (ODEs) that describe their evolution. This evolution can be represented as motion in the phase space spanned by the concentration variables of the chemical reaction. Transient decay corresponds to a collapse of the “compressible fluid” representing the continuum of possible dynamical states of the system. Collapse occurs sequentially through a hierarchy of nested, attracting, slow invariant manifolds (SIMs), i.e., sets that map into themselves under the action of the phase flow, eventually reaching the asymptotic attractor of the system. Using a symbolic manipulative language, explicit formulas for the SIMs can be found by iterating functional equations obtained from the system's ODEs. Iteration converges geometrically fast to a SIM at large concentrations and, if necessary, can be stabilized at small concentrations. Three different chemical models are examined in order to show how finding the SIM for a model depends on its underlying dynamics. For every model the iterative method provides a global SIM formula; however, formal series expansions for the SIM diverge in some models. Repelling SIMs can be also found by iterative methods because of the invariance of trajectory geometry under time reversal. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Bayesian predictive approach to interim monitoring in clinical trials
Authors: Dmitrienko Alexei , Wang Ming‐Dauh
Published: July 2005

This paper reviews Bayesian strategies for monitoring clinical trial data. It focuses on a Bayesian stochastic curtailment method based on the predictive probability of observing a clinically significant outcome at the scheduled end of the study given the observed data. The proposed method is applied to derive efficacy and futility stopping rules in clinical trials with continuous, normally distributed and binary endpoints. The sensitivity of the resulting stopping rules to the choice of prior distributions is examined and guidelines for choosing a prior distribution of the treatment effect are discussed. The Bayesian predictive approach is compared to the frequentist (conditional power) and mixed Bayesian‐frequentist (predictive power) approaches. The interim monitoring strategies discussed in the paper are illustrated using examples from a small proof‐of‐concept study and a large mortality trial. Copyright © 2005 John Wiley & Sons, Ltd.
Energy and pitch-angle dispersions of LLBL/cusp ions seen at middle altitudes: predictions by the open magnetosphere model
Authors: Lockwood M.
Published: July 2005

Abstract. Numerical simulations are presented of the ion distribution functions seen by middle-altitude spacecraft in the low-latitude boundary layer (LLBL) and cusp regions when reconnection is, or has recently been, taking place at the equatorial magnetopause. From the evolution of the distribution function with time elapsed since the field line was opened, both the observed energy/observation-time and pitch-angle/energy dispersions are well reproduced. Distribution functions showing a mixture of magnetosheath and magnetospheric ions, often thought to be a signature of the LLBL, are found on newly opened field lines as a natural consequence of the magnetopause effects on the ions and their flight times. In addition, it is shown that the extent of the source region of the magnetosheath ions that are detected by a satellite is a function of the sensitivity of the ion instrument . If the instrument one-count level is high (and/or solar-wind densities are low), the cusp ion precipitation detected comes from a localised region of the mid-latitude magnetopause (around the magnetic cusp), even though the reconnection takes place at the equatorial magnetopause. However, if the instrument sensitivity is high enough, then ions injected from a large segment of the dayside magnetosphere (in the relevant hemisphere) will be detected in the cusp. Ion precipitation classed as LLBL is shown to arise from the low-latitude magnetopause, irrespective of the instrument sensitivity. Adoption of threshold flux definitions has the same effect as instrument sensitivity in artificially restricting the apparent source regionKey words. Low-latitude boundary layer · Cusp regions · Open magnetosphere model · Mid-altitudes
Observations of flux rope − associated particle bursts with GEOTAIL in the distant tail
Authors: Belehaki A. , Sarris E. T. , Tsiropoula G. , McEntire R. W. , Kokubun S. , Yamamoto T.
Published: July 2005

Abstract. Geotail energetic particle, magnetic field data and plasma observations (EPIC, MGF and CPI experiments) have been examined for a number of energetic particle bursts in the distant tail (120Re<|XGSM|< 130 Re), associated with moving magnetic field structures, following substorm onsets. The features obtained from this data analysis are consistent with the distant magnetotail dynamics determined first by ISEE3 observations and explained in terms of the neutral line model. At the onset of the bursts, before plasma sheet entrance, energetic electrons appear as a field-aligned beam flowing in the tailward direction, followed by anisotropic ions. Within the flux rope region, suprathermal ions exhibit a convective anisotropy, which allows determination of the plasma flow velocity, assuming that the anisotropy arises from the Compton-Getting effect. The velocities thus determined in the plasma sheet are estimated to be 200–650 km/s, and compare favourably with the velocities derived from the CPI electron and proton experiment. The estimated length of magnetic field structures varies between 28 and 56 Re and depends on the strength of the westward electrojet intensification. Finally, the three structures reported here show clear magnetic field signatures of flux rope topology. The existence of a strong magnetic field aligned approximately along the Y-axis and centred on the north-to-south excursion of the field, and the bipolar signature in both By and/or Bz components, is consistent with the existence of closed field lines extending from Earth and wrapping around the core of the flux rope structure.Key words. Magnetospheric configuration and dynamics · Magnetotail
High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes
Authors: Wright D. M. , Yeoman T. K. , Chapman P. J.
Published: July 2005

Abstract. A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geographic: 69.6°N 19.2°E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100–400 s and have azimuthal wave numbers in the range 3–8. They are interpreted here as local field line resonances. Phase information provided by O- and X-mode Doppler data support the view that these are associated with field line resonances having large azimuthal scale sizes. The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generation of Doppler signatures from incident ULF waves. The outcome suggests that the dominant mechanism involved in producing the Doppler signature is the vertical component of an E × B bulk motion of the local plasma caused by the electric field perturbation of the ULF wave.Key words. Auroral ionosphere · Magnetosphere-ionosphere interactions · MHD waves and instabilities HF Doppler · ULF Waves
Parametrization of momentum and energy depositions from gravity waves generated by tropospheric hydrodynamic sources
Authors: Gavrilov N. M.
Published: July 2005

Abstract. The mechanism of generation of internal gravity waves (IGW) by mesoscale turbulence in the troposphere is considered. The equations that describe the generation of waves by hydrodynamic sources of momentum, heat and mass are derived. Calculations of amplitudes, wave energy fluxes, turbulent viscosities, and accelerations of the mean flow caused by IGWs generated in the troposphere are made. A comparison of different mechanisms of turbulence production in the atmosphere by IGWs shows that the nonlinear destruction of a primary IGW into a spectrum of secondary waves may provide additional dissipation of nonsaturated stable waves. The mean wind increases both the effectiveness of generation and dissipation of IGWs propagating in the direction of the wind. Competition of both effects may lead to the dominance of IGWs propagating upstream at long distances from tropospheric wave sources, and to the formation of eastward wave accelerations in summer and westward accelerations in winter near the mesopause.
Variations in Schumann resonances and their relation to atmospheric electric parameters at Nagycenk station
Authors: Märcz F. , Sátori G. , Zieger B.
Published: July 2005

Abstract. The present study is based on simultaneous measurements of the atmospheric electric potential gradient (PG) and Schumann resonances at Nagycenk station (Hungary) from 1993 to 1996. Annual and semi-annual variations detected previously in the relative amplitudes of Schumann resonances (SR) in the first three modes are confirmed by the extended data series applied here. The regular annual variation found in the PG (with winter maximum and summer minimum) is in the opposite phase, compared to that of the SR amplitudes. Nevertheless, even the PG (being a parameter of the DC global circuit) occasionally shows a distinct secondary peak in summer as indicated by the results of the present analysis (and corresponding to a recent study on further parameters of the DC global circuit). In spite of the presumed dominance of local influence over the global one, a suitable PG parameter correlates well with SR (representing the AC global circuit) on the annual time scale. It also became evident that a semi-annual variation (with spring and autumn maxima and winter and summer minima) is generally present in SR. Certain signatures of a semi-annual variation have also been revealed in the PG, however, the phase of this semi-annual variation does not fit the pattern shown by SR (and tropical surface air temperature, respectively). The representativeness of the PG data has also been checked by means of a single day's diurnal variations displaying a phase corresponding to that of the `Carnegie Curve'. Additionally, the coincidence of short-term changes (lasting some hours) both in the SR and the PG parameter is also demonstrated on a day disturbed by local factors. The results are discussed in the context of correlations between surface air temperature and parameters of the atmospheric electric global circuit shown by previous studies.
Theory of the photodissociation of ozone in the Hartley continuum: Potential energy surfaces, conical intersections, and photodissociation dynamics
Authors: Baloïtcha Ezinvi , Balint-Kurti Gabriel G.
Published: July 2005

Ab initio potential energy and transition dipole moment surfaces are presented for the five lowest singlet even symmetry electronic states of ozone. The surfaces are calculated using the complete active space self consistent field method followed by contracted multireference configuration interaction (MRCI) calculations. A slightly reduced augmented correlation consistent valence triple-zeta orbital basis set is used. The ground and excited state energies of the molecule have been computed at 9282 separate nuclear geometries. Cuts through the potential energy surfaces, which pass through the geometry of the minimum of the ground electronic state, show several closely avoided crossings. Close examination, and higher level calculations, very strongly suggests that some of these seemingly avoided crossings are in fact associated with non-symmetry related conical intersections. Diabatic potential energy and transition dipole moment surfaces are created from the computed ab initio adiabatic MRCI energies and transition dipole moments. The transition dipole moment connecting the ground electronic state to the diabatic B̃ state surface is by far the strongest. Vibrational-rotational wavefunctions and energies are computed using the ground electronic state. The energy level separations compare well with experimentally determined values. The ground vibrational state wavefunction is then used, together with the diabatic B̃←X transition dipole moment surface, to form an initial wavepacket. The analysis of the time-dependent quantum dynamics of this wavepacket provides the total and partial photodissociation cross sections for the system. Both the total absorption cross section and the predicted product quantum state distributions compare well with experimental observations. A discussion is also given as to how the observed alternation in product diatom rotational state populations might be explained.
Interstitial oxygen molecules in amorphous SiO2. I. Quantitative concentration analysis by thermal desorption, infrared photoluminescence, and vacuum-ultraviolet optical absorption
Authors: Kajihara Koichi , Hirano Masahiro , Uramoto Motoko , Morimoto Yukihiro , Skuja Linards , Hosono Hideo
Published: July 2005

The amount of oxygen molecules (O2) in amorphous SiO2(a-SiO2), also called interstitial O2, was quantitatively measured by combining thermal-desorption spectroscopy (TDS) with infrared photoluminescence (PL) measurements of interstitial O2 at 1272 nm while exciting with 1064-nm Nd: yttrium aluminum garnet laser light. It was found that the amount of O2 released by the TDS measurement is proportional to the intensity decrease of the PL band, demonstrating that a-SiO2 easily emits interstitial O2 during thermal annealing in vacuum. This correlation yielded the proportionality coefficient between the absolute concentration of interstitial O2 and its PL intensity normalized against the intensity of the fundamental Raman bands of a-SiO2. This relationship was further used to determine the optical-absorption cross section of the Schumann–Runge band of the interstitial O2 located at photon energies ≳6.5eV. This band is significantly redshifted and has a larger cross section compared to that of O2 in the gas phase.
Interstitial oxygen molecules in amorphous SiO2. II. The influence of common dopants (SiOH, SiF, and SiCl groups) and fictive temperature on the decay of singlet photoluminescence
Authors: Kajihara Koichi , Kamioka Hayato , Hirano Masahiro , Miura Taisuke , Skuja Linards , Hosono Hideo
Published: July 2005

Time decay of photoluminescence due to interstitial oxygen molecules (O2) in synthetic amorphous SiO2(a-SiO2) was studied by varying the fictive temperature and the concentrations of common dopants (SiOH, SiCl, and SiF groups). The decay constant is insensitive to the fictive temperature, but strongly depends on the type of dopants: it is reduced by the nonradiative decay via an energy transfer from O2 to the vibrational modes of the dopants. The increases in the nonradiative decay rate due to SiOH, SiF, and SiCl groups are strong, slight, and negligible, respectively, which correlates with their vibrational energies. The quantum yield decreases by ∼20% as the SiOH content increases from 1017 to 1020cm−3. The deviation from the single exponential decay is due to the shape variation in the a-SiO2 network cages that surround O2, and to the distance distribution between O2 and SiOH groups.
Interstitial oxygen molecules in amorphous SiO2. III. Measurements of dissolution kinetics, diffusion coefficient, and solubility by infrared photoluminescence
Authors: Kajihara Koichi , Kamioka Hayato , Hirano Masahiro , Miura Taisuke , Skuja Linards , Hosono Hideo
Published: July 2005

Concentration changes of interstitial oxygen molecules (O2) in amorphous SiO2(a-SiO2) thermally annealed in oxygen atmosphere were examined by the O2 photoluminescence at 1272 nm excited with 765-nm light of titanium sapphire laser. This highly sensitive technique allows the time- and temperature-dependent concentration changes of interstitial O2 due to their incorporation from an oxygen atmosphere to be directly measured. The data provide the dissolution rate, the diffusion coefficient, and the solubility of interstitial O2 in a-SiO2 and are able to exclude interferences from other forms of mobile oxygen species in a-SiO2. These observations confirm that O2 molecules are incorporated into a-SiO2 without separating into monoatomic species, diffuse in a-SiO2 without extensive interaction with the a-SiO2 network, and play a primary role in the thermal oxidation of silicon.
Robust and regenerable integrally gated carbon nanotube field emitter arrays
Authors: Hsu David S. Y. , Shaw Jonathan L.
Published: July 2005

We have grown multiwalled carbon nanotubes by chemical-vapor deposition on two types of gated structures, one containing a silicon post, and another having an open aperture. A gate current to anode-current ratio of 2.5%, the lowest of any nanotube field emitter arrays was measured for the open aperture configuration. The silicon post structures produced 1-nA emission current at gate voltages below 20V and up to 1mA at 40V (from 0.5-mm2 area). The emission was relatively stable compared to other field emitter arrays and destructive arcing was not observed. The gate voltage needed to produce a given emission current was reduced by adsorbed water vapor and was unaffected by xenon. Emission in hydrogen at pressures near 10−4Torr also increased the emission current, and restored a large fraction of the original emission current to arrays degraded by operation in oxygen. Electron energy distributions broaden and shift to lower energies at higher emission current. The broadening can be explained by the potentials developed at the silicon-nanotube contacts, and at the nanotube-vacuum interface.
Photoelectron trapping in N2O 7σ→kσ resonant ionization
Authors: Rathbone G. J. , Poliakoff E. D. , Bozek John D. , Toffoli Daniele , Lucchese R. R.
Published: July 2005

Vibrationally resolved photoelectron spectroscopy of the N2O+(AΣ+2) state is used to compare the dependence of the photoelectron dynamics on molecular geometry for two shape resonances in the same ionization channel. Spectra are acquired over the photon energy range of 18⩽hν⩽55eV. There are three single-channel resonances in this range, two in the 7σ→kσ channel and one in the 7σ→kπ channel. Vibrational branching ratio curves are determined by measuring vibrationally resolved photoelectron spectra as a function of photon energy, and theoretical branching ratio curves are generated via Schwinger variational scattering calculations. In the region 30⩽hν⩽40eV, there are two shape resonances (kσ and kπ). The kσ ionization resonance is clearly visible in vibrationally resolved measurements at hν=35eV, even though the total cross section in this channel is dwarfed by the cross section in the degenerate, more slowly varying 7σ→kπ channel. This kσ resonance is manifested in non-Franck–Condon behavior in the approximately antisymmetric ν3 stretching mode, but it is not visible in the branching ratio curve for the approximately symmetric ν1 stretch. The behavior of the 35-eV kσ resonance is compared to a previously studied N2O 7σ→kσ shape resonance at lower energy. The mode sensitivity of the 35-eV kσ resonance is the opposite of what was observed for the lower-energy resonance. The contrasting mode-specific behavior observed for the high- and low-energy 7σ→kσ resonances can be explained on the basis of the “approximate” symmetry of the quasibound photoelectron resonant wave function, and the contrasting behavior reflects differences in the continuum electron trapping. An examination of the geometry dependence of the photoelectron dipole matrix elements shows that the kσ resonances have qualitatively different dependences on the individual bond lengths. The low-energy resonance is influenced only by changes in the end-to-end length of the molecule, whereas the higher-energy resonance depends on the individual N–N and N–O bond lengths. Branching ratios are determined for several vibrational levels, including the symmetry-forbidden bending mode, and all of the observed behavior is explained in the context of an independent particle, Born–Oppenheimer framework.
Extraordinary emission from two-dimensional plasmonic-photonic crystals
Authors: Puscasu Irina , Pralle M. , McNeal M. , Daly J. , Greenwald A. , Johnson E. , Biswas R. , Ding C. G.
Published: July 2005

A metallodielectric architecture is employed to readily tailor the spectral properties of a bulk material for application to infrared sources and spectroscopic sensors. We exploit the interaction between surface plasmons at a metal interface with a photonic crystal in silicon to control the spectral response of the surface in reflection, absorption, and emission. The design uses Si-based thermally isolated suspended bridge structures fabricated using conventional photolithography techniques. The tunable narrow spectral response is defined by the symmetry and periodicity of the metallodielectric photonic crystal. Individual subresonances are recognized within this bandwidth. We model their origin through calculations of surface-plasmon modes in the metallic grating overlayer. Periodic arrays of holes in thin metal layers lead to coupled plasmons at the two metal–dielectric interfaces that, in turn, couple to modes in the underlying silicon–air photonic crystal. The model provides crucial physical insight into the interaction between surface plasmons and photonic crystals, with good agreement with the experimental results.
Unimolecular rovibrational bound and resonance states for large angular momentum: J=20 calculations for HO2
Authors: Zhang Hong , Smith Sean C.
Published: July 2005

We explore the calculation of unimolecular bound states and resonances for deep-well species at large angular momentum using a Chebychev filter diagonalization scheme incorporating doubling of the autocorrelation function as presented recently by Neumaier and Mandelshtam [Phys. Rev. Lett. 86, 5031 (2001)]. The method has been employed to compute the challenging J=20 bound and resonance states for the HO2 system. The methodology has firstly been tested for J=2 in comparison with previous calculations, and then extended to J=20 using a parallel computing strategy. The quantum J-specific unimolecular dissociation rates for HO2→H+O2 in the energy range from 2.114to2.596eV have been reported for the first time, and comparisons with the results of Troe and co-workers [J. Chem. Phys. 113, 11019 (2000) Phys. Chem. Chem. Phys. 2, 631 (2000)] from statistical adiabatic channel method/classical trajectory calculations have been made. For most of the energies, the reported statistical adiabatic channel method/classical trajectory rate constants agree well with the average of the fluctuating quantum-mechanical rates. Near the dissociation threshold, quantum rates fluctuate more severely, but their average is still in agreement with the statistical adiabatic channel method/classical trajectory results.
Field-effect mobility of polycrystalline tetrabenzoporphyrin thin-film transistors
Authors: Shea Patrick B. , Kanicki Jerzy , Ono Noboru
Published: July 2005

A possible relation between a thin-film microstructure and an organic thin-film field-effect transistor (OFET) behavior is discussed in terms of nonlinearity in the extraction of the device electrical parameters. Staggered source and drain electrode OFETs were fabricated using a soluble precursor form of the organic small molecule semiconductor tetrabenzoporphyrin, and characterized using linear and nonlinear best-fit methods. Linear best-fit models overestimated the field-effect mobility and accumulation threshold voltage when compared to a nonlinear best-fit model that accounts for dispersive charge-carrier transport. The deviation between the methods is found to be consistently less than that for polymer OFETs, as indicated by smaller nonlinearity factors of γ=1.2 and 1.7 in the linear and saturation regimes, respectively. The nonlinear field-effect mobility exhibits a sublinear gate-bias dependence wherein the mobility increases at a slower rate in strong accumulation than near threshold. Furthermore, nonlinear curve fitting indicates lower trap characteristic temperatures as compared to polymer OFETs, and a relatively moderate density of grain-boundary trap states localized at the dielectric interface and in the bulk to be filled before accumulation-related conduction dominates.
Plasmonics: Localization and guiding of electromagnetic energy in metal/dielectric structures
Authors: Maier Stefan A. , Atwater Harry A.
Published: July 2005

We review the basic physics of surface-plasmon excitations occurring at metal/dielectric interfaces with special emphasis on the possibility of using such excitations for the localization of electromagnetic energy in one, two, and three dimensions, in a context of applications in sensing and waveguiding for functional photonic devices. Localized plasmon resonances occurring in metallic nanoparticles are discussed both for single particles and particle ensembles, focusing on the generation of confined light fields enabling enhancement of Raman-scattering and nonlinear processes. We then survey the basic properties of interface plasmons propagating along flat boundaries of thin metallic films, with applications for waveguiding along patterned films, stripes, and nanowires. Interactions between plasmonic structures and optically active media are also discussed.
Effective electromechanical moduli of ferroelectric ceramics with fiber textures
Authors: Zhou Y. C. , Liu J. , Li J. Y.
Published: July 2005

In this letter, we report the predictions on the effective piezoelectric coefficients and electromechanical coupling factors of ferroelectric ceramics BaTiO3 and Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PMN-PT) with various fiber textures, including [001], [011], and [111], using a two-scale micromechanical model that accounts for microstructural phenomena at both domain and grain levels. It was observed that for BaTiO3 the [011] texture is optimal with highest d31 and d33, while for PMN-PT [001] texture is optimal despite the fact that [011]-oriented single-crystalline PMN-PT has higher d32 than that of [001]-oriented PMN-PT single crystal. In fact, [011]-textured PMN-PT ceramics have much smaller piezoelectric coefficients d32 and d33 than does [011]-oriented PMN-PT single crystal. It is also noted that [001]-textured BaTiO3 and PMN-PT ceramics have even higher electromechanical coupling factor k31 than that of [001]-oriented single crystals.
Deformation of a capsule in simple shear flow: Effect of membrane prestress
Authors: Lac Etienne , Barthès-Biesel Dominique
Published: July 2005

We investigate the effect of an initial isotropic prestress on the mechanics of a spherical capsule freely suspended in a simple shear flow. The capsule consists of a drop of liquid enclosed by a very thin hyperelastic membrane. A sufficient prestress may prevent the buckling instability that arises at low shear rates when the membrane bending resistance is neglected. A small perturbation analysis of the capsule deformation is first obtained for small prestress and weak viscous stresses. When the viscous shear stress and the preinflation are large, a numerical model of the capsule deformation shows how prestress decreases the capsule deformation for a given shear rate and how it significantly increases the elastic tension in the membrane at a given deformation level. These results may help the experimentalists to detect the presence of an osmotic pressure difference in a semipermeable capsule.
Overpoling-induced property degradation in Pb(Mg1∕3Nb2∕3)O3–PbTiO3 single crystals of near-morphotropic phase boundary compositions
Authors: Shanthi M. , Hoe K. H. , Lim C. Y. H. , Lim L. C.
Published: July 2005

Overpoling phenomenon has been observed in flux-grown Pb(Mg1∕3Nb2∕3)O3–(31–32)%PbTiO3 single crystals when poled above 0.4kV∕mm at room temperature. This leads to increased property variations at intermediate poling fields (0.6–0.8kV∕mm) and to the degradation of piezoelectric properties at high poling fields (⩾1.0kV∕mm). In comparison, both PMN–28%PT and PMN–30%PT crystal compositions are resistant to overpoling, of which PMN–30%PT exhibits superior dielectric and piezoelectric properties with KT≈7500–9000, d33≈2200–2500pC∕N, and d31≈1100–1400pC∕N. The electromechanical coupling factors (k33=0.90–0.94; k31=0.48–0.55, and kt=0.58–0.62) are relatively insensitive to the poling field and crystal composition.
Efficiency of multiple atom doping in wide band gap semiconductors
Authors: Miyazaki Takehide , Yamasaki Satoshi
Published: July 2005

We present a thermodynamic model calculation for the efficiency of an impurity-atom-complex formation suggested for doping of wide band gap semiconductors, where the complexes with various sizes coexist at local equilibrium as suggested by Van de Walle and Neugebauer [J. Appl. Phys. 95, 3851 (2004)]. When the size of a target complex becomes large, the effect of configurational entropy of smaller complexes shows up in the energetics and may even hamper stabilization of the target. Thus one should design a target complex with the size being as small as possible and the binding energy as large as possible, in order to make the concept of multiple atom doping a real technology.
In-plane strain distribution in the surface region of thin silicon overlayers on insulator
Authors: Omi Hiroo , Kawamura Tomoaki , Fujikawa Seiji , Tsusaka Yoshiyuki , Kagoshima Yasushi , Matsui Junji
Published: July 2005

A thin silicon nano-overlayer (SNOL) fabricated by oxidation and etchback in a separation by implantation of oxygen wafer was investigated by grazing incident x-ray diffraction at incident angles between 0.01° and 0.1° below the critical angle of total reflection (0.18° ). We measured {220} reflections by probing the sample in depth and found that the SNOL has finite domains under strain close to the surface. We also found that annealing the sample up to 1000 °C significantly reduced inhomogeneous in depth strain and increased the size of the domains in the surface region of the SNOL.
Selective excitation of tryptophan fluorescence decay in proteins using a subnanosecond 295nm light-emitting diode and time-correlated single-photon counting
Authors: McGuinness Colin D. , Sagoo Kulwinder , McLoskey David , Birch David J. S.
Published: July 2005

We demonstrate an AlGaN light-emitting diode (LED) giving pulses of ∼600ps full width half maximum, 0.35μW average power, 0.6mW peak power, and ∼12nm bandwidth at 295nm. This source is ideal for protein intrinsic tryptophan fluorescence decay research without the unwanted excitation of tyrosine and paves the way to lab-on-a-chip protein assays using fluorescence decay times. Fluorescence decay and anisotropy decay measurements of human serum albumin are reported and the usefulness of the 295nm LED demonstrated in comparisons with a nanosecond flashlamp and LEDs with nominal wavelength emission of 280nm.
Ambipolar Cu- and Fe-phthalocyanine single-crystal field-effect transistors
Authors: de Boer R. W. I. , Stassen A. F. , Craciun M. F. , Mulder C. L. , Molinari A. , Rogge S. , Morpurgo A. F.
Published: July 2005

We report the observation of ambipolar transport in field-effect transistors fabricated on single crystals of copper- and iron-phthalocyanine, using gold as a high work-function metal for the fabrication of source and drain electrodes. In these devices, the room-temperature mobility of holes reaches 0.3cm2∕Vs in both materials. The highest mobility for electrons is observed for iron-phthalocyanines and is approximately one order of magnitude lower. Our measurements indicate that these values are limited by extrinsic contact effects due to the transistor fabrication and suggest that considerably higher values for the electron and hole mobility can be achieved in these materials.
Single-layer organic memory devices based on N,N′-di(naphthalene-l-yl)-N,N′-diphenyl-benzidine
Authors: Chen Jiangshan , Ma Dongge
Published: July 2005

We report a single-layer organic electrically bistable device made of N,N′-di(naphthalene-l-yl)-N,N′-diphenyl-benzidine sandwiched between two electrodes. The measured current-voltage characteristics show two states of different conductivities at the same applied voltage—high-conductance state (ON state) and low-conductance state (OFF state)—and the two states are reproducible by applying a negative writing voltage. It was found that the ratio of the ON∕OFF current depends strongly on the writing voltage, and the bistable characteristics were yet retained for up to hours and days before reading the device after applying a writing voltage. Furthermore, more than 106 write-read-erase-reread cycles have been performed in ambient conditions without degradation. These properties show the devices promising for high-density, low-cost memory application.
Enhanced thermoelectric performance in PbTe-based superlattice structures from reduction of lattice thermal conductivity
Authors: Caylor J. C. , Coonley K. , Stuart J. , Colpitts T. , Venkatasubramanian R.
Published: July 2005

We have fabricated two-dimensional n-type PbTe∕PbTe0.75Se0.25 structures using an evaporation process. In optimized films exhibiting a high-quality superlattice structure, a significant reduction in lattice thermal conductivity has been experimentally measured. The reduction would indicate enhanced thermoelectric device performance compared to standard PbTeSe alloys given that the electrical components, specifically, the Seebeck coefficient and electrical resistivity, were not observed to deteriorate from bulk values. The analysis of these films shows continuous layers with a true two-dimensional superlattice structure, as opposed to the PbTe∕PbSe system that exhibits zero-dimensional structures from self-assembly. The room-temperature measurement of cross-plane figure-of-merit in a n-type PbTe∕PbTe0.75Se0.25 device structure by the transient method has been combined with temperature-dependent measurements of in-plane resistivity and Seebeck coefficient to yield evidence of enhanced thermoelectric performance. The similarities and differences between the superlattice in the PbTe∕PbTe0.75Se0.25 system and the Bi2Te3∕Sb2Te3 material system are presented.
Ballistic thermal and electrical conductance measurements on individual multiwall carbon nanotubes
Authors: Brown Elisabetta , Hao Ling , Gallop John C. , Macfarlane John C.
Published: July 2005

We report thermal measurements on individual carbon nanotubes using a temperature sensing scanned microscope probe. An arc-grown bundle of multiwalled nanotubes (MWNTs) is mechanically attached to a thermal probe. The heat flow down individual MWNTs is recorded as a function of the temperature difference across them. Simultaneous measurements of thermal and electrical conductance are recorded. The size of the conductance steps observed at room temperature and the correlation between electrical and thermal conductance steps are discussed and we present evidence for ballistic transport of both phonons and electrons in these tubes.
Mechanisms of refractive index modification during femtosecond laser writing of waveguides in alkaline lead-oxide silicate glass
Authors: Vega F. , Armengol J. , Diez-Blanco V. , Siegel J. , Solis J. , Barcones B. , Pérez-Rodríguez A. , Loza-Alvarez P.
Published: July 2005

We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond laser irradiation of an alkaline lead-oxide silicate glass. MicroRaman spectroscopy and nonlinear fluorescence were employed to probe the local glass network structure and the formation of optically active defects respectively. At low laser pulse energies, the laser modified region is formed by a single light guiding region, whereas for pulses above 14 μJ the modified region is formed by a central dark zone, which does not guide light, accompanied by light guiding zones located in the surrounding of the dark one. This behavior is different from that observed in common silica glass systems but agrees with recent results obtained in phosphate and heavy metal oxide glasses. However, our results show that, unlike the latter glass, local densification of the glass occurs in the whole laser modified region, i.e., in the dark and the guiding zones. The suppression of light guiding in the dark region is explained by a high density of absorbing color centers.
Bulk cohesive energy and surface tension from the size-dependent evaporation study of nanoparticles
Authors: Nanda K. K.
Published: July 2005

In this letter, it is shown that the bulk cohesive energy (EB) and bulk surface tension (γ) can be deduced from the size-dependent evaporation (SDE) study of free nanoparticles. The surface tension of nanoparticles (γn) is obtained by analyzing SDE data on the basis of the Kelvin equation, while EB is obtained by reanalyzing the SDE data. By comparing the size-dependent melting and the SDE of nanoparticles, γ is evaluated.
Flexible semitransparent pentacene thin-film transistors with polymer dielectric layers and NiOx electrodes
Authors: Lee Jiyoul , Hwang D. K. , Choi Jeong-M. , Lee Kimoon , Kim Jae Hoon , Im Seongil , Park Ji Hoon , Kim Eugene
Published: July 2005

We have fabricated the flexible semitransparent pentacene-based thin-film transistors (TFTs) with poly-4-vinylphenol (PVP) dielectric layers which were deposited by spin coating on a thermostable plastic substrate with a conductive film. For the source∕drain (S∕D) electrodes of our flexible pentacene TFTs both Au and semitransparent NiOx have been tested. It was found that NiOx was better matched to the pentacene channel for the S∕D contacts than Au. Our flexible pentacene TFTs with semitransparent NiOx contacts exhibited mobility of ∼0.24cm2∕Vs higher than that achieved with Au contacts (∼0.14cm2∕Vs) and also demonstrated a higher initial drain current.
Suppressing the thermal lens effect by magnetic-field-induced mass transfer and phase separation in a magnetic fluid
Authors: Pu Shengli , Chen Xianfeng , Chen Lijun , Liao Weijun , Chen Yuping , Xia Yuxing
Published: July 2005

A method for suppressing the thermal lens effect in a magnetic fluid is proposed in this letter. When an external parallel magnetic field is applied, the thermal lens effect is weakened, and the degree of the divergence of the laser beam after passing through the magnetic fluid decreases. By experimental measurement and theoretical analysis, we assign this phenomenon to two physical mechanisms: the magnetic-field-induced mass transfer and phase separation in the magnetic fluid. With this method, the quality of the magnetic-fluid-based potential photonic devices can be improved.
Characterization of highly (110)- and (111)-oriented Pb(Zr,Ti)O3 films on BaPbO3 electrode using Ru conducting barrier
Authors: Liang Chun-Sheng , Wu Jenn-Ming
Published: July 2005

Highly non-(001)-oriented Pb(Zr,Ti)O3 (PZT) films have been fabricated by rf-magnetron sputtering. The preferential (110)-oriented BaPbO3 (BPO) deposited on Ru buffer layer induces the growth of (110)-oriented PZT film. With the aid of self-organized growth of PZT, the orientation of the film deposited on random-oriented BPO∕Pt(111)∕Ru(002) is (111)-preferred. The insertion of Pt layer between BPO and Ru changes the orientation of PZT from (110) to (111) and prevents the oxygen diffusion. These non-(001)-oriented PZT films possess more superior ferroelectric, fatigue, and retention properties than those of (001)-oriented PZT films.
Single-cell Raman and fluorescence microscopy reveal the association of lipid bodies with phagosomes in leukocytes
Authors: van Manen Henk-Jan , Kraan Yvonne M. , Roos Dirk , Otto Cees
Published: July 2005

Cellular imaging techniques based on vibrational spectroscopy have become powerful tools in cell biology because the molecular composition of subcellular compartments can be visualized without the need for labeling. Using high-resolution, nonresonant confocal Raman microscopy on individual cells, we demonstrate here that lipid bodies (LBs) rich in arachidonate as revealed by their Raman spectra associate with latex bead-containing phagosomes in neutrophilic granulocytes. This finding was corroborated in macrophages and in PLB-985 cells, which can be induced to differentiate into neutrophil-like cells, by selective staining of LBs and visualization by confocal fluorescence microscopy. We further show that the accumulation of LBs near phagosomes is mediated at least in part by the flavohemoprotein gp91phox(in which “phox” is phagocyte oxidase), because different LB distributions around phagocytosed latex beads were observed in WT and gp91phox-deficient PLB-985 cells. gp91phox, which accumulates in the phagosomal membrane, is the catalytic subunit of the leukocyte NADPH oxidase, a critical enzyme in the innate immune response. Finally, time-lapse fluorescence microscopy experiments on neutrophils revealed that the LB-phagosome association is transient, similar to the “kiss-and-run” behavior displayed by endosomes involved in phagosome maturation. Because arachidonic acid (AA) has been shown to be involved in NADPH oxidase activation and phagosome maturation in neutrophils and macrophages, respectively, the findings reported here suggest that LBs may provide a reservoir of AA for local activation of these essential leukocyte functions.