bluuebunny/crossref_metadata_2025 huggingface dataset:
On the problem of periodicity and hidden solitons for the KdV model
Authors: Engelbrecht Jüri , Salupere Andrus
Published: March 2005

In continuum limit, the Fermi-Pasta-Ulam lattice is modeled by a Korteweg–de Vries (KdV) equation. It is shown that the long-time behavior of a KdV soliton train emerging from a harmonic excitation has a regular periodicity of right- and left-going trajectories. In a soliton train not all the solitons are visible, the solitons with smaller amplitude are hidden and their influence is seen through the changes of phase shifts of larger solitons. In the case of an external harmonic force several resonance schemes are revealed where both visible and hidden solitons have important roles. The weak, moderate, strong, and dominating fields are distinguished and the corresponding solution types presented.
Functional determinants for the Dirac equation with mixed pseudodifferential boundary conditions over finite cylinders
Authors: Loya Paul , Park Jinsung
Published: March 2005

In this note, we explicitly compute the functional determinant of a Dirac Laplacian with nonlocal pseudodifferential boundary conditions over a finite cylinder in terms of the ζ-function of the Dirac operator on the cross section and the pseudodifferential operators defining the boundary conditions. In particular, this result reduces to our previous formula [J. Phys. AJPHAC5 37, 7381 (2004)] for the special case of generalized Atiyah–Patodi–Singer conditions. To prove our main result, we use the gluing and comparison formulas established by the present authors in Refs 14 and 15.
A special class in vanishing helicity ideal flows
Authors: Eshraghi Homayoon , Abedini Yousefali
Published: March 2005

The derivation of a Lagrangian invariant so-called spirality is reviewed through the Lagrangian coordinates. The value of the spirality is fixed up to a gauge transformation. The helicity conservation follows directly from this invariant. Among all ideal flows with zero helicity in a domain of flow frozen into the fluid motion, a special class is introduced. This special topological class has the possibility to transform its spirality to be identically zero everywhere in the domain. For those simply connected domains of motion, a necessary and a sufficient condition is presented for these zero spirality flows.
Nontopological bare solutions in the relativistic self-dual Maxwell–Chern–Simons–Higgs model
Authors: Han Jongmin , Jang Jaeduk
Published: March 2005

In this paper we prove the existence of the radially symmetric nontopological bare solutions in the relativistic self-dual Maxwell–Chern–Simons–Higgs model. We also verify the Chern–Simons limit for those solutions.
Fermi–Pasta–Ulam, solitons and the fabric of nonlinear and computational science: History, synergetics, and visiometrics
Authors: Zabusky Norman J.
Published: March 2005

This paper is mostly a history of the early years of nonlinear and computational physics and mathematics. I trace how the counterintuitive result of near-recurrence to an initial condition in the first scientific digital computer simulation led to the discovery of the soliton in a later computer simulation. The 1955 report by Fermi, Pasta, and Ulam (FPU) described their simulation of a one-dimensional nonlinear lattice which did not show energy equipartition. The 1965 paper by Zabusky and Kruskalshowed that the Korteweg–de Vries (KdV) nonlinear partial differential equation, a long wavelength model of the α-lattice (or cubic nonlinearity), derived by Kruskal, gave quantitatively the same results obtained by FPU. In 1967, Zabusky and Deem showed that a localized short wavelength initial excitation (then called an “optical” and now a “zone-boundary mode” excitation ) of the α-lattice revealed “n-curve” coherent states. If the initial amplitude was sufficiently large energy equipartition followed in a short time. The work of Kruskal and Miura (KM), Gardner and Greene (GG), and myself led to the appreciation of the infinity of denumerable invariants (conservation laws) for Hamiltonian systems and to a procedure by GGKM in 1967 for solving KdV exactly. The nonlinear science field exponentiated in diversity of linkages (as described in Appendix A). Included were pure and applied mathematics and all branches of basic and applied physics, including the first nonhydrodynamic application to optical solitons, as described in a brief essay (Appendix B) by Hasegawa. The growth was also manifest in the number of meetings held and institutes founded, as described briefly in Appendix D. Physicists and mathematicians in Japan, USA, and USSR (in the latter two, people associated with plasma physics) contributed to the diversification of the nonlinear paradigm which continues worldwide to the present. The last part of the paper (and Appendix C) discuss visiometrics: the visualization and quantification of simulation data, e.g., projection to lower dimensions, to facilitate understanding of nonlinear phenomena for modeling and prediction (or design). Finally, I present some recent developments that are linked to my early work by: Dritschel (vortex dynamics via contour dynamics/surgery in two and three dimensions); Friedland (pattern formation by synchronization in Hamiltonian nonlinear wave, vortex, plasma, systems, etc.); and the author (“n-curve” states and energy equipartition in a FPU lattice).
Thickness effects of Al0.5Ga0.5N barriers on the optical properties of δ-AlGaN-inserted GaN-coupled multiquantum wells
Authors: Park Y. S. , Park C. M. , Lee S. J. , Kang T. W. , Lee S. H. , Oh Jae-Eung
Published: March 2005

Coupled multiquantum well structures, GaN(10Å)∕AlGaN(5Å)∕GaN(20Å) bounded by Al0.5Ga0.5N barriers whose thickness varied from 20to100Å, are characterized by photoluminescence and cathodoluminescence measurements. As a result of these measurements, main emission lines are redshifted with increments of the Al0.5Ga0.5N barrier thickness. The main emission line of photoluminescence for the barrier thickness of 20Å is centered at 3.188eV. This value is redshifted with respect to the GaN excitonic emission line by an amount of 290meV. An additional redshift centered at 2.96eV is observed with the barrier thickness of 100Å. As the excitation power increases, the main emission lines of the photoluminescence are blueshifted significantly and then saturated. This behavior is explained by the partial screening of the piezoelectric field by the photoexcited electron-hole pairs. From the results of cathodoluminescence measurements, the GaN excitonic emission line as well as the quantum well emission line for the barrier thickness of 20Å is also observed.
Electron spin resonance g tensors for complexes of Ne and Ar with AlO: Theoretical studies related to the large matrix effect observed for AlO
Authors: Grein Friedrich
Published: March 2005

For Nen–AlO (n=2, 4, 6, 8, 10) and Arn–AlO clusters (n=2, 4, 6, 8), the perpendicular (relative to AlO) component of the g tensor was calculated by second-order perturbation theory, using multireference configuration-interaction wave functions. The rare-gas (Rg) atoms were placed axially and/or off axially (one or two rings of four Rg atoms each), and the distance of the Rg atoms from the Al and O atoms, or from the AlO axis, was varied from 4 to 12 bohrs. Rg atoms placed axially mostly increase g⊥, whereas off-axially placed ones lower it below the gas-phase value of AlO. The largest deviations from g⊥ of isolated AlO occur at Ne–Al,O distances of 5–6 bohrs, and Ar–Al,O distances of 6–9 bohrs, with maximal lowerings of about 1600 ppm for Ne and about 2200 ppm (estimated) for Ar in the case of two axial and eight off-axial Rg atoms. Electron spin resonance studies by Knight and Weltner found large matrix effects for AlO, with downshifts of g⊥ observed to be about 450 and 1150 ppm in Ne and Ar matrices, respectively.
Restricted rotational motion of CO in a protein internal cavity: Evidence for nonseparating correlation functions from IR pump-probe spectroscopy
Authors: Helbing Jan , Nienhaus Karin , Nienhaus G. Ulrich , Hamm Peter
Published: March 2005

The strongly restricted orientational motion of CO molecules trapped in the Xe4 internal cavity of myoglobin mutant L29W-S108L is investigated by polarization-dependent mid-infrared pump-probe spectroscopy at cryogenic temperatures. Following an ultrafast initial decay, the signal anisotropy reaches an asymptotic value that is significantly larger than the prediction from the well-known relation r=25⟨P2[μ⃗(0)∙μ⃗(τ)]⟩, based on previously established potential parameters. This discrepancy is explained by showing that the full four-point correlation function describing third-order spectroscopy ⟨μ⃗(0)μ⃗(0)μ⃗(τ)μ⃗(τ+t)⟩ does not factorize in systems where its fast decay is dominated by restricted reorientation of the transition dipole moments.
The XΣg+1, BΔg1, and B′Σg+1 states of C2: A comparison of renormalized coupled-cluster and multireference methods with full configuration interaction benchmarks
Authors: Sherrill C. David , Piecuch Piotr
Published: March 2005

Unusual bonding and electronic near degeneracies make the lowest-lying singlet states of the C2 molecule particularly challenging for electronic structure theory. Here we compare two alternative approaches to modeling bond-breaking reactions and excited states: sophisticated multireference configuration interaction and multireference perturbation theory methods, and a more “black box,” single-reference approach, the completely renormalized coupled-cluster method. These approximate methods are assessed in light of their ability to reproduce the full configuration interaction potential energy curves for the XΣg+1, BΔg1, and B′Σg+1 states of C2, which are numerically exact solutions of the electronic Schrödinger equation within the space spanned by a 6-31G* basis set. Both the multireference methods and the completely renormalized coupled-cluster approach provide dramatic improvements over the standard single-reference methods. The multireference methods are nearly as reliable for this challenging test case as for simpler reactions which break only single bonds. The completely renormalized coupled-cluster approach has difficulty for large internuclear separations R in this case, but over the wide range of R=1.0–2.0Å, it compares favorably with the more complicated multireference methods.
Reactive scattering dynamics in atom+polyatomic systems: F+C2H6→HF(v,J)+C2H5
Authors: Whitney Erin S. , Zolot Alexander M. , McCoy Anne B. , Francisco Joseph S. , Nesbitt David J.
Published: March 2005

State-to-state scattering dynamics of F+C2H6→HF(v,J)+C2H5 have been investigated at Ecom=3.2(6)kcal∕mol under single-collision conditions, via detection of nascent rovibrationally resolved HF(v,J) product states with high-resolution infrared laser absorption methods. State-resolved Doppler absorption profiles are recorded for multiple HF(v,J) transitions originating in the v=0,1,2,3 manifold, analyzed to yield absolute column-integrated densities via known HF transition moments, and converted into nascent probabilities via density-to-flux analysis. The spectral resolution of the probe laser also permits Doppler study of translational energy release into quantum-state-resolved HF fragments, which reveals a remarkable linear correlation between (i) HF(v,J) translational recoil and (ii) the remaining energy available, Eavail=Etot−EHF(v,J). The dynamics are interpreted in the context of a simple impulsive model based on conservation of linear∕angular momentum that yields predictions in good agreement with experiment. Deviations from the model indicate only minor excitation of ethyl vibrations, in contrast with a picture of extensive intramolecular vibrational energy flow but consistent with Franck–Condon excitation of the methylene CH2 bending mode. The results suggest a relatively simple dynamical picture for exothermic atom+polyatomic scattering, i.e., that of early barrier dynamics in atom+diatom systems but modified by impulsive recoil coupling at the transition state between translational∕rotational degrees of freedom.
Controlling the heat flow: Now it is possible
Authors: Casati Giulio
Published: March 2005

We discuss the problem of heat conduction in 1D nonlinear chains in relation to the dynamical properties of the system. We provide convincing numerical evidence for the validity of Fourier law of heat conduction in linear mixing systems. Therefore, deterministic diffusion and normal heat transport which are usually associated with full hyperbolicity, actually take place in systems without exponential instability. We then show that, acting on the parameter which controls the strength of the on site potential inside a segment of the chain, we induce a transition from conducting to insulating behavior in the whole system. The control of heat conduction by nonlinearity opens the possibility to propose new devices such as a thermal rectifier.
Acoustic-phonon dispersion in nanowires
Authors: Mukdadi Osama M. , Datta Subhendu K. , Dunn Martin L.
Published: March 2005

We study phonon dispersion in layered prismatic nanowires that can have an arbitrary cross-sectional geometry. We calculate phonon dispersion using a hybrid analytical/numerical approach that models propagation along the wire analytically, but deformation in the plane of the cross section using the finite element method. In our results we consider only two layers, but the calculational approach is applicable to multiple layers.
SrTa 2 O 6 thin films for high-K dielectric applications grown by chemical vapor deposition on different substrates
Authors: Regnery Stephan , Thomas Reji , Ehrhart Peter , Waser Rainer
Published: March 2005

SrTa 2 O 6 thin films with thickness between 6 and 150 nm were deposited by metal-organic chemical vapor deposition in a multiwafer planetary reactor. The monomolecular precursor, strontium-tantalum-(methoxyethoxy)-ethoxide, was dissolved in toluene and injected by a liquid delivery system. A rather narrow process window for the deposition of stoichiometric SrTa2O6 was found for this precursor at low pressures and a susceptor temperature around 500 °C. Films were grown on Pt∕TiO2∕SiO2∕Si, TiNx∕Si, and SiO2∕Si substrates. The as-deposited films were x-ray amorphous and could be crystallized by postannealing at a temperature ⩾700°C. The distorted tetragonal tungsten bronze phase of SrTa2O6 was dominating within a broad range of compositions (Sr∕Ta: 0.4–0.7) and a perovskite-type phase was additionally observed for Sr∕Ta>0.7 and predominated for Sr∕Ta>1. The electrical properties have been investigated with metal-insulator-metal and metal-insulator-semiconductor capacitors after sputter deposition of Pt top electrodes. The amorphous films had a dielectric constant K in the range of 35–45 and low leakage currents. For stoichiometric SrTa2O6 the dielectric permittivity reached values of K=100–110, but the leakage currents were increased. Remarkably, the permittivity is not very sensitive to deviations from the exact stoichiometry of the SrTa2O6 phase (Sr∕Ta: 0.4–0.7), but a decrease to values of K=30–40 is observed along with the transition to the perovskite phase at high Sr contents.
Measuring propagation loss in a multimode semiconductor waveguide
Authors: De Rossi Alfredo , Ortiz Valentin , Calligaro Michel , Lanco Loïc , Ducci Sara , Berger Vincent , Sagnes Isabelle
Published: March 2005

The measurement of propagation loss based on the Fabry–Pérot transmission fringes is a powerful tool for the characterization of single-mode optical waveguides. This method is well established for lithium niobate waveguides, but its implementation with semiconductor devices is more delicate. A method to extend this technique to the case of multimode semiconductor waveguides is presented. Our procedure involves Fabry–Pérot measurements on a large spectral range, in order to find an interval where multimode effects do not alter the loss measurement. Two experimental examples are given, showing also the domain of validity of this approach.
Piezoelectric characterization and thermal stability of a high-performance α-quartz-type material, gallium arsenate
Authors: Cambon Olivier , Haines Julien , Fraysse Guillaume , Détaint Jacques , Capelle Bernard , Van der Lee Arie
Published: March 2005

Piezoelectric measurements were performed on large single crystals (8 mm along the c direction) of an α-quartz-type piezoelectric material, gallium arsenate, GaAsO4, which allow us to extend the structure-property relationships in the α-quartz-type materials. These first measurements on Y-rotated-cut plates have shown that gallium arsenate is the highest-performance piezoelectric material of this group. As compared to the coupling coefficients of the other materials with the same structure (kSiO2=8%, kAlPO4=11%, and kGaPO4=16%), gallium arsenate exhibits the highest piezoelectric coupling coefficient of about 22%, as has been predicted by the structure-property relationships. Moreover, from these piezoelectric measurements, the C66′ elastic constant was determined and compared with elastic constants in quartz-type materials. The proposed value for the cut angle of the AT plane in GaAsO4 is −6.3°. In order to extend the previous thermal stability results, thermal gravimetric analysis (TGA) and x-ray diffraction have been carried out on GaAsO4 powder at high temperatures. It has been shown that GaAsO4 is stable up to 1030 °C. The thermal-expansion coefficient of GaAsO4 is 4.0×10−5K−1. The thermal expansion of the predicted AT plane (Y−6.3°) in GaAsO4 is shown to be similar to that of the other materials. Finally, it is demonstrated that the intertetrahedral bridging angle θ (A–O–B) of GaAsO4 is the most stable in α-quartz materials, which enables one to predict that GaAsO4 should retain high piezoelectric performances up to 925 °C.
Structure of the nonionic surfactant triethoxy monooctylether C8E3 adsorbed at the free water surface, as seen from surface tension measurements and Monte Carlo simulations
Authors: Paszternák András , Kiss Éva , Jedlovszky Pál
Published: March 2005

The adsorption layer of the nonionic surfactant triethoxy monooctylether C8E3 has been investigated at the free water surface by means of both experimental and computer simulation methods. The surface tension of the aqueous solution of C8E3 has been measured by pendant drop shape analysis in the entire concentration range in which C8E3 is soluble in water. The data obtained from these measurements are used to derive the adsorption isotherm. The critical micellar concentration and the surface excess concentration of the saturated adsorption layer are found to be 7.48 mM and 4.03μmol∕m2, respectively, the latter value corresponding to the average area per molecule of 41Å2. In order to analyze the molecular level structure of the unsaturated adsorption layer, Monte Carlo simulations have been performed at four different surface concentration values, i.e., 0.68, 1.36, 2.04, and 2.72μmol∕m2, respectively. It has been found that the water surface is already almost fully covered at the lowest surface density value investigated, and the adsorbed molecules show a strong preference for lying parallel with the interface in elongated conformations. No sign of the penetration of the hydrophilic triethoxy headgroups into the aqueous phase to any extent has been observed. With increasing surface densities the preferential orientation of the apolar octyl tails gradually turns from lying parallel with the interface to pointing toward the vapor phase by their CH3 end, whereas the conformation of the adsorbed molecules becomes gradually less elongated. Both of these changes lead to the increase of the number of C8E3 molecules being in a direct contact (i.e., forming hydrogen bonds) with water. However, the increasing number of the C8E3 molecules hydrogen bonded to water is found to be accompanied by the weakening of this binding, i.e., the decrease of both the number of hydrogen bonds a bound C8E3 molecule forms with water and the magnitude of the average binding energy of the adsorbed C8E3 molecules.
A method for the analysis of multiphase bonding structures in amorphous SiOxNy films
Authors: Cova P. , Poulin S. , Grenier O. , Masut R. A.
Published: March 2005

A tetrahedral model is presented to explain the bonding properties of nonstoichiometric amorphous silicon oxynitride (a-SiOxNy) alloys, grown under highly nonequilibrium conditions, whose structures obey neither the random bonding model nor the random mixture model. Based on our approach, a numerical procedure is proposed to obtain the relative atomic percentages of each component structural phase from the deconvolution of the high-resolution x-ray photoelectron spectroscopy (XPS) spectra in the Si 2p3∕2 region. The tetrahedral model is then used to study the bonding properties of a-SiOxNy films grown by electron-cyclotron resonance plasma-enhanced chemical-vapor deposition, having relatively low values of the O/Si atomic ratio (⩽0.37) incorporated in their networks. The experimental results show that five tetrahedral phases (tetrahedrons Si–Si4, Si–Si2ON, Si–N4, Si–Si3O, and Si–O4) are present in a-SiOxNy films with low N/Si atomic ratios (⩽0.93), while only three phases (Si–SiON2, Si–N4, and Si–O2N2) are present in samples with higher N/Si atomic ratios (⩾1.12). The Si3N4 phase is the most important bonding unit and it is the only phase present in all our samples. These results are corroborated by survey scans and by comparison with the high-resolution XPS spectra in the N 1s region. They support the validity of the model proposed for a-SiOxNy alloys and the XPS analysis, correlated with growth conditions, presented in this work.
Investigation of femtosecond laser assisted nano and microscale modifications in lithium niobate
Authors: Deshpande Devesh C. , Malshe Ajay P. , Stach Eric A. , Radmilovic Velimir , Alexander Dennis , Doerr David , Hirt Drew
Published: March 2005

A study of the physicochemical modifications at micro and nano scales as a result of femtosecond laser processing is essential to explore the viability of this process to write surface and subsurface structures in transparent media. To this end, scanning probe and transmission electron microscopy and spectroscopy techniques were used to study these modifications in lithium niobate. A variable power Ti:Sapphire system (800nm,300fs) was used to determine the ablation threshold of (110) lithium niobate, and to write these structures in the substrate for subsequent analysis. Higher processing energies were used to amplify the laser-induced effects for a clear understanding. Evidences of a number of simultaneously occurring mechanisms such as melting, ablation, and shockwave propagation are observed in the scanning electron microscope (SEM) micrographs. X-ray diffraction (XRD), Auger and electron dispersive spectroscopy (EDS) studies indicate loss of lithium and oxygen from the immediate surface of the processed region. Raman spectroscopy analysis indicates an unchanged chemical composition in the bulk, though at a loss of crystallinity. The surface and subsurface damage structures display a different nature of the amorphous and damaged material subregions, as observed in the respective transmission electron microscopy micrographs. A variation in oxygen counts is observed in the amorphous subregions, indicative of oxygen liberation and elemental segregation during the process. The oblate subsurface structure contains a void at the top, indicative of localized explosive melting and rapid quenching of the affected material. Thus, femtosecond laser writing produces different structures on the surface and the subsurface of the material. These results provide physicochemical insight towards writing chemically and spatially precise structures using femtosecond lasers, and will have direct implications in optical memory and waveguide writing and related applications.
Reflectance difference spectroscopy microscope for nanometer step height detection
Authors: Zhang Weifeng , Qin Zongyi , Yang Z.
Published: March 2005

A reflectance difference spectroscopy (RDS) microscope with 3-nm step height resolution and subwavelength lateral resolution for exposed surfaces and 5-nm step height resolution for interfaces 45nm beneath a transparent layer with smooth surface, is demonstrated. It has extremely high tolerance to optical path drift (up to 3.7μm at wavelength of 512nm), high tolerance to power fluctuation (∼5%), and a long working distance (8mm). Better height resolution can be achieved with higher laser power. The RDS signal that reveals the presence of the edges is due to the depolarization of light caused by scattering by the edges, so edges of any orientation can be detected with equal sensitivity without the need to rotate the sample.
Nanoscale morphological and electrical homogeneity of HfO2 and ZrO2 thin films studied by conducting atomic-force microscopy
Authors: Kremmer S. , Wurmbauer H. , Teichert C. , Tallarida G. , Spiga S. , Wiemer C. , Fanciulli M.
Published: March 2005

The morphological and electrical evolution of HfO2 and ZrO2 thin films is investigated on the nanoscale using conducting atomic-force microscopy in ultrahigh vacuum. Films of different thicknesses have been grown by atomic layer deposition. With increasing film thickness the film structure changes from amorphous to polycrystalline. By conducting atomic-force microscopy using local current–voltage curve statistics and two-dimensional current imaging it is found that the formation of crystallites has different effects on the electrical properties of the two dielectrics. In the case of HfO2, the crystalline fraction causes weak spots in the oxide, whereas for the ZrO2 films the crystallites exhibit lower leakage currents compared to the amorphous matrix and leakage is mainly determined by thickness fluctuations.
High mobility of a three-dimensional hole gas in parabolic quantum wells grown on GaAs(311)A substrates
Authors: Lamas T. E. , Quivy A. A. , Sergio C. S. , Gusev G. M. , Portal J. C.
Published: March 2005

The transport properties of a three-dimensional hole gas were investigated in wide parabolic quantum wells grown by molecular beam epitaxy on top of GaAs(311)A substrates. The p-type doping was performed using silicon and the parabolic potential was achieved with the digital-alloy technique. Hall-effect and Shubnikov–de Haas measurements carried out at low temperature revealed that the carrier mobility was more than twice higher than the one usually obtained from similar samples grown on GaAs(100) substrates using beryllium.
Complex impedance as a diagnostic tool for characterizing thermal detectors
Authors: Vaillancourt John E.
Published: March 2005

The complex ac impedance of a bolometer or microcalorimeter detector is easily measured and can be used to determine thermal time constants, thermal resistances, heat capacities, and sensitivities. Accurately extracting this information requires an understanding of the electrical and thermal properties of both the detector and the measurement system. We show that this is a practical method for measuring parameters in detectors with moderately complex thermal systems.
A closed ion source with a cylindrical repeller for sensitivity enhancement in quadrupole mass spectrometry
Authors: Park Chang J. , Ahn Jong R.
Published: March 2005

Sensitivity improvement has been achieved for a quadrupole mass spectrometer by replacing the flat repeller of a conventional ion source with a cylindrical repeller. Computer simulation of ion trajectories in the ion source demonstrated that ions were focused into the center of the ion lens with the cylindrical repeller but that ions were defocused with the flat repeller. Ion sources with the two repellers were tested for performance comparison using both a laboratory-built mass spectrometer and a commercial mass spectrometer. The cylindrical repeller showed about threefold sensitivity enhancement at lower repeller voltages across the mass range from 69to502m∕z.
Efficient charge collection in hybrid polymer/TiO2 solar cells using poly(ethylenedioxythiophene)/polystyrene sulphonate as hole collector
Authors: Ravirajan P. , Bradley D. D. C. , Nelson J. , Haque S. A. , Durrant J. R. , Smit H. J. P. , Kroon J. M.
Published: March 2005

We report a study of the optimization of power conversion efficiency in hybrid solar cells based on nanostructured titanium dioxide and a poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) based conjugated polymer. Charge collection efficiency is enhanced by introducing a poly(ethylenedioxythiophene)/polystyrene sulphonate (PEDOT) layer (under the gold electrode) as the hole collector. Device performance is maximized for a device with a net active layer thickness of 100 nm. The optimized device has peak external quantum efficiencies ≈40% at the polymer’s maximum absorption wavelength and yield short circuit current density ⩾2mAcm−2 for air mass (AM) 1.5 conditions (100mWcm−2, 1 sun). The AM 1.5 open circuit voltage for this device is 0.64 V and the fill factor is 0.43, resulting in an overall power conversion efficiency of 0.58%.
Hybrid light-emitting polymer device fabricated on a metallic nanowire array
Authors: Strevens A. E. , Drury A. , Lipson S. M. , Kröll M. , Blau W. J. , Hörhold H. H.
Published: March 2005

An electrode comprised of a copper nanowire array, fabricated by electrodeposition into a porous alumina membrane, is incorporated into a single-layer organic light-emitting device. The 48-nm-diameter copper nanowires form an array of electrical nanocontacts. Current–voltage and electroluminescence data for this device type are presented and compared with an equivalent planar copper electrode device. The nanowire array electrode device sustained a higher operating current density. The results show that such an array electrode can be used to inject charge in a polymer light-emitting diode, opening up the possibility of producing arrays of nanosized light sources using this approach.
Efficiency enhancement of an organic light-emitting diode with a cathode forming two-dimensional periodic hole array
Authors: Liu C. , Kamaev V. , Vardeny Z. V.
Published: March 2005

We fabricated an organic light-emitting diode using a π-conjugated polymer emissive layer sandwiched between two semitransparent electrodes: an optically thin gold film anode, whereas the cathode was in the form of an optically thick aluminum (Al) film with patterned periodic subwavelength two-dimensional hole array that showed anomalous transmission in the spectral range of the polymer photoluminescence band. At similar current densities, we obtained a sevenfold electroluminescence efficiency enhancement with the patterned Al device compared with a control device based on unperforated Al electrode.
Self-heated fiber Bragg grating sensors
Authors: Chen Kevin P. , McMillen Ben , Buric Michael , Jewart Chuck , Xu Wei
Published: March 2005

This letter demonstrates an approach for tuning fiber Bragg grating sensors with optical energy carried in the same optical fiber. Optical energy carried in the optical fiber was used to heat in-fiber Bragg gratings in order to alter the grating’s optical response to surrounding media. The functional enhancement of optically heated Bragg gratings as sensor devices is demonstrated by a dual-function Bragg grating temperature and level sensing array for liquid at room and cryogenic temperatures.
Surface-charge-induced asymmetric electrokinetic transport in confined silicon nanochannels
Authors: Qiao R. , Aluru N. R.
Published: March 2005

Molecular dynamics simulations of a NaF solution transport in a confined silicon nanochannel indicated that the water flux and the ionic conductivity through two oppositely charged silicon channels, that are otherwise similar, differ by a factor of more than three, and the co-ion fluxes are in the opposite direction. Such a behavior cannot be predicted by the classical electrokinetic transport theory, and is found to originate from the asymmetric dependence of the transport properties of water near the charged silicon surface.
Experimental demonstration of pseudomorphic heterojunction bipolar transistors with cutoff frequencies above 600GHz
Authors: Hafez Walid , Feng Milton
Published: March 2005

Pseudomorphic InP∕InGaAs heterojunction bipolar transistors (PHBTs) using a compositionally graded collector (10% indium grading) and graded base (6% indium grading) to reduce the transit time of the device are reported. A 0.4×6μm2 HBT achieves excellent ƒT values of 604GHz (associated ƒMAX=246GHz) at a collector current density of 16.8mA∕μm2, with a dc gain of 65 and a breakdown voltage of BVCEO=1.7V.
Plasticity of face processing in infancy
Authors: Pascalis O. , Scott L. S. , Kelly D. J. , Shannon R. W. , Nicholson E. , Coleman M. , Nelson C. A.
Published: March 2005

Experience plays a crucial role for the normal development of many perceptual and cognitive functions, such as speech perception. For example, between 6 and 10 months of age, the infant's ability to discriminate among native speech sounds improves, whereas the ability to discriminate among foreign speech sounds declines. However, a recent investigation suggests that some experience with nonnative languages from 9 months of age facilitates the maintenance of this ability at 12 months. Nelson has suggested that the systems underlying face processing may be similarly sculpted by experience with different kinds of faces. In the current investigation, we demonstrate that, in human infants between 6 and 9 months of age, exposure to nonnative faces, in this case, faces of Barbary macaques (
Macaca sylvanus
), facilitates the discrimination of monkey faces, an ability that is otherwise lost around 9 months of age. These data support, and further elucidate, the role of early experience in the development of face processing.
Simulation of workflow balancing in assembly shopfloor operations
Authors: Rajakumar S. , Arunachalam V.P. , Selladurai V.
Published: March 2005

Purpose

To provide a new model to solve the assembly‐planning problem of a textile machine in a shopfloor which can help researchers and practitioners.

Design/methodology/approach

The assembly planning of a textile machine (repetitive manufacturing system) involves the allocation of operations to cross‐trained operators. Workflow is defined as the workloads assigned to the operators. Operators with smaller workloads are selected to be assigned new operations from the list of unscheduled operations. Three different scheduling strategies – random, shortest processing time, and longest processing time – are adopted for the selection of operations to be assigned to operators. Different combinations of these strategies are considered for the selection of both preceding and succeeding operations. A computer simulation program has been coded on an IBM/PC‐compatible system in the C++ language to study the performance of real data from the shopfloor.

Findings

The relative percentage of imbalance is adopted for evaluating the performance of these heuristics. The RL, SL and LL produced well balanced workload schedules with lesser RPI values for all operators other than heuristics.

Research limitations/implications

Non‐traditional approaches like genetic algorithms can be applied to determine the robustness of the results obtained by this research.

Practical implications

The experiments on simulated and real data clearly indicate that the order of succeeding operations determines the balanced workflows to the assembly of operations among the operators.

Originality/value

The allocation of assembly operations to the operators is modeled into a parallel machine‐scheduling problem with precedence constraints using the objective of minimizing the workflow among the operators.
Comparing white matter lesions on T2 and FLAIR MRI in the Sydney Older Persons Study
Authors: Piguet O. , Ridley L. J. , Grayson D. A. , Bennett H. P. , Creasey H. , Lye T. C. , Anthony Broe G.
Published: March 2005

There is suggestion that magnetic resonance imaging (MRI) fluid‐attenuated inversion recovery (FLAIR) sequence may be more accurate than T2 images in detecting white matter lesions (WML) in older people. Comparative ratings of these two image sequences have not been directly investigated in very old individuals to date. We compared the ratings of periventricular and deep WML on these two sequences in a sample of 111 community dwellers (mean age 85.5 years) using semiquantitative methods. Periventricular WML were as commonly detected on T2 as on FLAIR but were more severely rated on the latter sequence. No such bias was observed for the deep WML. With one exception, correlations between the two sets of measures were significant at the P < 0.001 level (range: 0.34–0.75). Intrarater reliability coefficients were moderate to excellent for most ratings. These results suggest that ratings performed on T2‐weighted images to detect WML in very old individuals are very comparable with those performed on FLAIR images although FLAIR may allow a finer grading of periventricular lesions. Absence of FLAIR does not preclude the identification of WML in this population. These findings have clinical and epidemiological relevance where the acquisition of supplementary MRI data may not always be possible.
Clinical features, risk factors, and prognosis in transient global amnesia: a follow‐up study
Authors: Pantoni L. , Bertini E. , Lamassa M. , Pracucci G. , Inzitari D.
Published: March 2005

We previously observed a high frequency of psychopathological features in transient global amnesia (TGA). We aimed at assessing differences in risk factor profile and prognosis between TGA and transient ischemic attack (TIA) patients with a focus on aspects with possible psychopathological relevance. We studied 51 TGA patients (mean age ± SD, 62.7 ± 6.7 years; M/F = 24/27) and 51 control patients with TIA (mean age ± SD, 63.8 ± 6.7 years; M/F = 41/10) and followed them up for about 7 years. Compared with TIA controls, TGA patients more frequently had a history of psychiatric diseases (age and sex‐corrected OR = 2.86, 95% CI: 1.01–8.05) and alcohol use (OR = 3.26, 95% CI: 1.10–9.66) and less frequently a history of cardiac (OR = 0.29, 95% CI: 0.11–0.76) or peripheral artery disease (OR = 0.11, 95% CI: 0.01–0.96). A family history of psychiatric diseases was reported more frequently by TGA than TIA patients (OR = 2.99, 95% CI: 1.04–8.59). On follow‐up, in comparison with TIA patients, TGA patients had a significantly lower risk of combined stroke, myocardial infarct, and death (log‐rank test, P = 0.0059). In the multivariate analysis, the dissimilar baseline risk factor profile explained most of the difference in prognosis between the two groups. In comparison with TIA patients, patients with TGA have more frequently a personal or family history of psychiatric diseases and a more favorable vascular risk factor profile and prognosis. These results have therapeutic implications and reinforce the hypothesis that TGA is a benign disorder.
Effects of intraperitoneal injection of Rofecoxib in a mouse model of ALS
Authors: Azari M. F. , Profyris C. , Le Grande M. R. , Lopes E. C. , Hirst J. , Petratos S. , Cheema S. S.
Published: March 2005

There is increasing evidence that inflammatory mechanisms are involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). Inhibition of a key mediator of inflammation, cyclooxygenase 2 (COX‐2), represents a promising therapeutic approach in ALS. Here we tested the in vivo effects of a specific COX‐2 inhibitor, Rofecoxib, administered by intraperitoneal injection, in the SOD1G93A G1H mouse model of the familial form of ALS (fALS). Rofecoxib administration commenced at postnatal day 60 (P60), since the hallmarks of inflammation in the spinal cord were found to occur beyond this time‐point in this mouse model of fALS. We found a significant but small delay in the onset of locomotor impairment in mice treated with Rofecoxib at the dose of 10 mg/kg of weight. However, survival was not effected by treatment. As prostaglandin E2 levels in spinal cord or in plasma were not reduced by Rofecoxib treatment, these results may suggest lack of sufficient bioavailability as the reason for the modest clinical changes observed.
Clinical and genetic study on a new Chinese family with benign familial infantile seizures
Authors: Xiao B. , Deng F.‐Y. , Xiong G. , Wang K. , Zhang J. , Chen X.‐D. , Liu Y.‐Z. , Deng H.‐W.
Published: March 2005

Three loci for benign familial infantile seizures (BFIS, traditionally named benign familial infantile convulsions) have been mapped to the chromosome regions of 19q12–13.1, 2q24, and 16p12‐q12. We characterized the clinical features of a newly discovered Chinese family with BFIS and investigated whether it is linked to these loci. A four‐generation Chinese family was investigated and nineteen family members were examined. Fourteen microsatellite markers covering the three BFIS loci on the chromosome regions of 19q12–13.1, 2q24, and 16p12‐q12 were genotyped. Linkage analysis was performed. The main clinical features of our patients include onset of afebrile seizures between 3 and 10 months, normal psychomotor development, normal interictal electroencephalogram (EEG), and autosomal dominant inheritance. Magnetic resonance imaging (MRI) changes were found in the proband. Two‐point LOD scores are <−2.0 at the recombination rate of 0.0 for all the markers on the 2q24 region. Multipoint LOD scores are <−3.0 for the regions of 19q12–13.1 and 16p12–q12. Linkage analysis showed no evidence that the disease gene of this BFIS family is linked to the chromosome regions previously identified as the critical regions of the disease. Another chromosome region harboring the disease gene may exist in the new Chinese family.
Angiotensin II regulation of ovine fetoplacental artery endothelial functions: interactions with nitric oxide
Authors: Zheng Jing , Bird Ian M. , Chen Dong‐Bao , Magness Ronald R.
Published: March 2005

During normal pregnancy, elevated angiotensin II (Ang II) concentrations in the maternal and fetal circulations are associated with dramatic increases in placental angiogenesis and blood flow. Much is known about a local renin–angiotensin system within the uteroplacental vasculature. However, the roles of Ang II in regulating fetoplacental vascular functions are less well defined. In the fetal placenta, the overall in vivo vasoconstrictor responses of the blood vessels to Ang II infusion is thought to be less than that in its maternal counterpart, even though infused Ang II induces vasoconstriction. Recent data from our laboratories suggest that Ang II stimulates cell proliferation and increases endothelial nitric oxide synthase (eNOS) and production of nitric oxide (NO) in ovine fetoplacental artery endothelial cells. These data imply that elevations of the known vasoconstrictor Ang II in the fetal circulation may indeed play a role in the marked increases in fetoplacental angiogenesis and that Ang II‐elevated endothelial NO production may partly attenuate Ang II‐induced vasoconstriction on vascular smooth muscle. Together with both of these processes, the high levels of Ang II in the fetal circulation may serve to modulate overall fetoplacental vascular resistance. In this article, we review currently available data on the expression of Ang II receptors in the ovine fetal placenta with particular emphasis on the effects of Ang II on ovine fetoplacental endothelium. The potential cellular mechanisms underlying the regulation of Ang II on endothelial growth and vasodilator production are discussed.
Maternal nutrient restriction in sheep: hypertension and decreased nephron number in offspring at 9 months of age
Authors: Gilbert Jeffrey S. , Lang Alvin L. , Grant Angela R. , Nijland Mark J.
Published: March 2005

Pregnant ewes were fed either a 50% nutrient‐restricted (NR; n= 8) or a control 100% (C; n= 8) diet from day 28 to day 78 of gestation (dGA; term = 150 dGA). Lambs were born naturally, and fed to appetite throughout the study period. At 245 ± 1 days postnatal age (DPNA), offspring were instrumented for blood pressure measurements, with tissue collection at 270 DPNA. Protein expression was assessed using Western blot, glomerulus number determined via acid maceration and hormone changes by radioimmunoassay (RIA) or enzyme‐linked immunosorbent assay (ELISA). NR lambs had higher mean arterial pressure (MAP; 89.0 ± 6.6 versus 73.4 ± 1.6 mmHg; P < 0.05), fewer renal glomeruli (57.8 ± 23.8 versus 64.6 ± 19.3 × 104; P < 0.05), increased expression of angiotensin converting enzyme (ACE) in the renal cortex (942 ± 130 versus 464 ± 60 arbitrary pixel units (apu); P < 0.03), and increased angiotensin II receptor AT2 expression in the renal medulla (63.3 ± 12.1 versus 19.5 ± 44.2 × 104 apu; P < 0.03). All data are presented as mean ±s.e.m. The present data indicate that global maternal nutrient restriction (50%) during early to mid‐gestation impairs renal nephrogenesis, increases MAP, and alters expression of AT2 and ACE without an associated change in birth weight. These data demonstrate the existence of a critical window of fetal susceptibility during early to mid‐gestation that alters kidney development and blood pressure regulation in later life.
β‐Adrenoceptor‐mediated long‐term up‐regulation of the release machinery at rat cerebellar GABAergic synapses
Authors: Saitow Fumihito , Suzuki Hidenori , Konishi Shiro
Published: March 2005

Properly regulated interactions among excitatory and inhibitory synapses are critical for brain function. Compared to excitatory synapses, much less is known about the gain control mechanisms at inhibitory synapses. Herein we report a mechanism of noradrenergic long‐term potentiation (LTP) at inhibitory synapses following presynaptic β‐adrenoceptor activation. Stimulation of β‐adrenoceptors elicited LTP of GABA release from terminals of cerebellar interneurones. This action was dependent on the cAMP/protein kinase A signalling cascade and independent of the β‐adrenoceptor‐mediated acceleration of hyperpolarization‐activated cyclic nucleotide‐gated cation (HCN) channel. Furthermore, the β‐adrenoceptor‐ and protein kinase A‐mediated LTP was triggered by enhancement of the Ca2+ sensitivity of the release machinery and increase in the readily releasable pool. β‐Adrenoceptor activation also accelerated the recruitment of GABA into the releasable pool and enhanced synchronous and asynchronous release of GABA from the presynaptic terminal. Thus, the up‐regulation of GABA release machinery mediated by noradrenaline and β‐adrenoceptor activation provides a likely mechanism of feedforward inhibition of the cerebellar output neurone Purkinje cell, leading to a profound effect on motor control and learning associated with the cerebellum.
Reversals of anticipatory postural adjustments during voluntary sway in humans
Authors: Krishnamoorthy Vijaya , Latash Mark L.
Published: March 2005

We describe reversals of anticipatory postural adjustments (APAs) with the phase of a voluntary cyclic whole‐body sway movement. Subjects (n= 9) held a standard load in extended arms and released it by a bilateral shoulder abduction motion in a self‐paced manner at different phases of the sway. The load release task was also performed during quiet stance in three positions: in the middle of the sway range and close to its extreme forward and backward positions. Larger APAs were seen during the sway task as compared to quiet stance. Although the direction of postural perturbation associated with the load release was always the same, the direction of the APAs in the leg muscles reversed when the subjects were close to the extreme forward position as compared to the APAs in other phases and during quiet stance. The trunk muscles showed smaller APA modulation at the extreme positions but larger modulation when passing through the middle position, depending on the direction of sway, forward or backward. The phenomenon of APA reversals emphasizes the important role of safety in the generation of postural adjustments associated with voluntary movements. Based on these findings, APAs could be defined as changes in the activity of postural muscles associated with a predictable perturbation that act to provide maximal safety of the postural task component.