bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment and validation of a screened Coulomb hybrid density functional
Authors: Heyd Jochen , Scuseria Gustavo E.
Published: April 2004

This paper presents a revised and improved version of the Heyd–Scuseria–Ernzerhof screened Coulomb hybrid functional. The performance of this functional is assessed on a variety of molecules for the prediction of enthalpies of formation, geometries, and vibrational frequencies, yielding results as good as or better than the successful PBE0 hybrid functional. Results for ionization potentials and electron affinities are of slightly lower quality but are still acceptable. The comprehensive test results presented here validate our assumption that the screened, short-range Hartree–Fock (HF) exchange exhibits all physically relevant properties of the full HF exchange. Thus, hybrids can be constructed which neglect the computationally demanding long-range part of HF exchange while still retaining the superior accuracy of hybrid functionals, compared to pure density functionals.
Picosecond IR–UV pump–probe spectroscopic study of the dynamics of the vibrational relaxation of jet-cooled phenol. I. Intramolecular vibrational energy redistribution of the OH and CH stretching vibrations of bare phenol
Authors: Yamada Yuji , Ebata Takayuki , Kayano Masakazu , Mikami Naohiko
Published: April 2004

The intramolecular vibrational energy redistribution (IVR) of the OH stretching vibration of jet-cooled phenol-h6 (C6H5OH) and phenol-d5 (C6D5OH) in the electronic ground state has been investigated by picosecond time-resolved IR–UV pump–probe spectroscopy. The OH stretching vibration of phenol was excited with a picosecond IR laser pulse, and the subsequent temporal evolutions of the initially excited level and the redistributed ones due to the IVR were observed by multiphoton ionization detection with a picosecond UV pulse. The IVR lifetime for the OH stretch vibration of phenol-h6 was determined to be 14 ps, while that of the OH stretch for phenol-d5 was found to be 80 ps. This remarkable change of the IVR rate constant upon the dueteration of the CH groups strongly suggests that the “doorway states” for the IVR from the OH level would be the vibrational states involving the CH stretching modes. We also investigated the IVR rate of the CH stretching vibration for phenol-h6. It was found that the IVR lifetime of the CH stretch is less than 5 ps. The fast IVR is described by the strong anharmonic resonance of the CH stretch with many other combinations or overtone bands.
Picosecond IR–UV pump–probe spectroscopic study of the dynamics of the vibrational relaxation of jet-cooled phenol. II. Intracluster vibrational energy redistribution of the OH stretching vibration of hydrogen-bonded clusters
Authors: Kayano Masakazu , Ebata Takayuki , Yamada Yuji , Mikami Naohiko
Published: April 2004

A picosecond time-resolved IR–UV pump–probe spectroscopic study has been carried out for investigating the intracluster vibrational energy redistribution (IVR) and subsequent dissociation of hydrogen-bonded clusters of phenol (C6H5OH) and partially deuterated phenol (C6D5OH, phenol-d5) with various solvent molecules. The H-bonded OH stretching vibration was pumped by a picosecond IR pulse, and the transient S1–S0 UV spectra from the pumped level as well as the redistributed levels were observed with a picosecond UV laser. Two types of hydrogen-bonded clusters were investigated with respect to the effect of the H-bonding strength on the energy flow process: the first is of a strong “σ-type H-bond” such as phenol-(dimethyl ether)n=1 and phenol dimer, and the second is phenol-(ethylene)n=1 having a weak “π-type H-bond.” It was found that the population of the IR-pumped OH level exhibits a single-exponential decay, whose rate increases with the H-bond strength. On the other hand, the transient UV spectrum due to the redistributed levels showed a different time evolutions at different monitoring UV frequency. From an analysis of the time profiles of the transient UV spectra, the following three-step scheme has been proposed for describing the energy flow starting from the IVR of the initially excited H-bonded OH stretching level to the dissociation of the H bond. (1) The intramolecular vibrational energy redistribution takes place within the phenolic site, preparing a hot phenol. (2) The energy flows from the hot phenol to the intermolecular vibrational modes of the cluster. (3) Finally, the hydrogen bond dissociates. Among the three steps, the rate constant of the first step was strongly dependent on the H-bond strength, while the rate constants of the other two steps were almost independent of the H-bond strength. For the dissociation of the hydrogen bond, the observed rate constants were compared with those calculated by the Rice, Ramsperger, Kassel, and Marcus model. The result suggests that dissociation of the hydrogen bond takes place much faster than complete energy randomization within the clusters.
Temperature dependent exciton emission from herringbone aggregates of conjugated oligomers
Authors: Spano Frank C.
Published: April 2004

In this work, the effect of temperature, exciton bandwidth, and size on the photoluminescence spectra of defect-free two-dimensional herringbone aggregates of π-conjugated oligomers such as oligophenylene vinylene and oligothiophene is investigated theoretically. The model is based on exciton-phonon coupling in two-dimensional herringbone lattices with the exciton deriving from the lowest optical (1Ag→1Bu) transition and the phonon from the most strongly coupled intramolecular vibrational mode with frequency ω0. Simple analytical expressions are obtained for the line strengths of the emission origin (0-0) and first replica (0-1) as a function of the number of molecules comprising the aggregate, N, the free exciton bandwidth, WD, and the temperature, T. At a given temperature, the 0-0 emission intensity initially scales as N/Nth, where Nth is the superradiant threshold number, but eventually converges to NT/Nth, where NT is the size independent thermal coherence number. NT is inversely proportional to temperature and proportional to the exciton band curvature (ωc) near the band bottom; NT=1+4πωc/kbT. In striking contrast, the 0-1 line strength is relatively insensitive to temperature and size, but scales as the inverse square of WD+ω0. The insensitivity of the first replica to the exciton coherence number makes the ratio of the 0-0 to 0-1 line strengths a measure of the exciton coherence number. The ratio can be used to test for crystal purity. Comparison to experiments on thin films of quaterthiophene shows that the thermal coherence size is given by NT≈1+450/T (K) and that superradiance, which requires NT>Nth, can only be observed at temperatures less than 1 K.
Electronic states of linear Au clusters supported on metal surfaces: Why are they like those of a particle in a box?
Authors: Mills Greg , Wang Bing , Ho Wilson , Metiu Horia
Published: April 2004

Scanning tunneling spectroscopy and microscopy show that the empty states of linear Au clusters supported on a metal surface behave as if they are the states of an electron in an empty one-dimensional box. We show here that certain difficulties of this description are removed by a particle-in-a-cylinder model. This interpretation is supported by density functional calculations.
Semiclassical dynamics of the van der Waals states in O3(X 1A1)
Authors: Joyeux Marc , Schinke Reinhard , Grebenshchikov Sergy Yu.
Published: April 2004

We present the analysis and the semiclassical quantization of the van der Waals states of ozone in the ground electronic state X 1A1. Progressions of these states dominate the spectrum of O3 at threshold. Periodic orbits are used to perform assignment and quantization of the vibrational states. Semiclassical quantization is numerically accurate despite the fact that the classical phase space is chaotic while the nodal patterns of the quantum mechanical wave functions are regular. The lifetimes of recombination of the van der Waals states into the “normal” ozone are also discussed.
A multimode analysis of the gas-phase photoelectron spectra in oligoacenes
Authors: Malagoli M. , Coropceanu V. , da Silva Filho D. A. , Brédas J. L.
Published: April 2004

We present a multimode vibrational analysis of the gas-phase ultraviolet photoelectron spectra of the first ionization in anthracene, tetracene, and pentacene, using electron-vibration constants computed at the density functional theory level. The first ionization of each molecule exhibits a high-frequency vibronic structure; it is shown that this regularly spaced feature is actually the consequence of the collective action of several vibrational modes rather than the result of the interaction with a single mode. We interpret this feature in terms of the missing mode effect. We also discuss the vibronic coupling constants and relaxation energies obtained from the fit of the photoelectron spectra with the linear vibronic model.
Variationally stable calculations for molecular systems: Polarizabilities and two-photon ionization cross section for the hydrogen molecule
Authors: Machado Andréa M. , Masili Mauro
Published: April 2004

The variationally stable method of Gao and Starace [B. Gao and A. F. Starace, Phys. Rev. Lett. 61, 404 (1988); Phys. Rev. A 39, 4550 (1989)] has been applied for the first time to the study of multiphoton processes in molecular systems. The generalization in theory is presented, as well as the calculation of properties such as the static and dynamic polarizabilities of the hydrogen molecule and the generalized two-photon ionization cross section. The Schwinger variational iterative method [R. R. Lucchese and V. McKoy, Phys. Rev. A 21, 112 (1980)] has been applied in the achievement of the photoelectron wave function, while a Hartree–Fock representation has been used for the target. This research has been motivated by the scarceness of ab initio calculations of molecular multiphoton ionization cross sections in the literature.
Molecular dynamics simulation study on the phase behavior of the Gay–Berne model with a terminal dipole and a flexible tail
Authors: Fukunaga Hiroo , Takimoto Jun-ichi , Doi Masao
Published: April 2004

To study the effect of the alkyl tail and the terminal dipole on the stability of the liquid crystalline phase of mesogens, we have carried out molecular dynamics simulations for 1CB(4-methyl-4′-cyanobiphenyl) and 5CB(4-n-pentyl-4′-cyanobiphenyl) by using a coarse-grained model. In the coarse-grained model, a 5CB molecule is divided into the rigid part of 1CB moiety, which is represented by an ellipsoid, and the remaining flexible part which is represented by a chain of united atoms. The nonbonded potential between coarse-grained segments is represented by the generalized Gay–Berne (GB) potential and the potential parameters are determined by directly comparing the GB potential with the atomistic potentials averaged over the rotation of the mesogen around its axis. In addition, a dipole moment is placed at one end of the ellipsoid opposite to the flexible tail. The ordered state obtained in the polar 5CB model was assigned as the nematic phase, and the experimental static and dynamical properties were reproduced well by using this coarse-grained model. Both the dipole–dipole interactions and the thermal fluctuation of the flexible tail increase the positional disorder in the director direction, and stabilize the nematic phase. Thus, the nematic phase in the polar 5CB is induced by a cooperative effect of the flexible tail and the terminal dipole. It is noted that a local bilayer structure with head-to-head association is formed in the nematic phase, as experimentally observed by x-ray diffraction measurements.
New approach to the first-order phase transition of Lennard-Jones fluids
Authors: Muguruma Chizuru , Okamoto Yuko , Mikami Masuhiro
Published: April 2004

The multicanonical Monte Carlo method is applied to a bulk Lennard-Jones fluid system to investigate the liquid–solid phase transition. We take the example of a system of 108 argon particles. The multicanonical weight factor we determined turned out to be reliable for the energy range between −7.0 and −4.0 kJ/mol, which corresponds to the temperature range between 60 and 250 K. The expectation values of the thermodynamic quantities obtained from the multicanonical production run by the reweighting techniques exhibit the characteristics of first-order phase transitions between liquid and solid states around 150 K. The present study reveals that the multicanonical algorithm is particularly suitable for analyzing the transition state of the first-order phase transition in detail.
Determining the adsorptive and catalytic properties of strained metal surfaces using adsorption-induced stress
Authors: Pala Raj Ganesh S. , Liu Feng
Published: April 2004

We demonstrate a model for determining the adsorptive and catalytic properties of strained metal surfaces based on linear elastic theory, using first-principles calculations of CO adsorption on Au and K surfaces and CO dissociation on Ru surface. The model involves a single calculation of the adsorption-induced surface stress on the unstrained metal surface, which determines quantitatively how adsorption energy changes with external strain. The model is generally applicable to both transition- and non-transition-metal surfaces, as well as to different adsorption sites on the same surface. Extending the model to both the reactant and transition state of surface reactions should allow determination of the effect of strain on surface reactivity.
Radiation damage of biosystems mediated by secondary electrons: Resonant precursors for uracil molecules
Authors: Gianturco F. A. , Lucchese R. R.
Published: April 2004

Calculations are presented for the energy locations and spatial structures of low-energy resonant states describing transient negative ions (TNIs) of the uracil molecule in the gas phase. The resonant states are modeled using scattering calculations of low energy electrons interacting with isolated molecules in their equilibrium geometry. The interaction forces used in this model are described in detail. Examination of the spatial densities of the excess resonant electrons for the various TNIs found by the calculations allows one to associate the metastable anions with specific features of the experimentally observed fragmentation patterns.
Tunable effective interactions between dendritic macromolecules
Authors: Götze I. O. , Harreis H. M. , Likos C. N.
Published: April 2004

We employ extensive Monte Carlo and molecular-dynamics simulations to investigate the effective interactions between the centers of mass of dendritic macromolecules of variable flexibility and generation number. Two different models for the connectivity and steric interactions between the monomers are employed, the first one being purely entropic in nature and the second explicitly involving energetic interactions. We find that the effective potentials have a generic Gaussian shape, whose range and strength can be tuned via modifications in the generation number and flexibility of the spacers. We supplement our simulation analysis by a density-functional approach in which the connectivity between the monomers is approximated by an external confining potential that holds the monomer beads together. Using a simple density functional for the interactions between the monomers, we find semiquantitative agreement between theory and simulation. The implications of our findings for the interpretation of scattering data from concentrated dendrimer solutions are also discussed.
In situ high-resolution transmission electron microscopy observation of photodecomposition process of poly-hydrocarbons on catalytic TiO2 films
Authors: Yoshida Kenta , Yamasaki Jun , Tanaka Nobuo
Published: April 2004

Photocatalytic TiO2 materials have been one of the strong subjects of investigation for these ten years among various kinds of advanced functional materials. For studying the catalytic reaction by physical science techniques, a kind of transmission electron microscope technique is presented and applied to the study of photocatalysis on TiO2 films by UV light. Using the technique, we visualized in situ the decomposition process of hydrocarbons deposited on the TiO2 films in atomic level and elucidated a mechanism of the decomposition process.
Dynamics and the breaking of a driven cage: I2 in solid Ar
Authors: Bihary Z. , Zadoyan R. , Karavitis M. , Apkarian V. A.
Published: April 2004

Pump–probe measurements of I2 in solid Ar are reported and analyzed to extract a description of cage response to impulsive excitation, from the gentle kick, up to the breaking point. The most informative data are obtained through wavepacket motion on cage-bound, but otherwise dissociative, potentials where the chromophore acts as a transducer to drive the cage and to report on the local dynamics. This general class of dynamics is identified and analyzed as a function of energy in Ar, Kr, and Xe. The overdriven cage rebounds with a characteristic period of 1.2 ps that shows little dependence on excitation amplitude in all hosts. After rebound, the cage rings as a local resonant mode in Ar, with a period of 1 ps and dephasing time of 3 ps. This mode remains at the Debye edge in Kr and Xe, with periods of 630 and 800 fs, and dephasing times of 8 and 6 ps, respectively. In the bound B-state, the cage fluctuates toward its dilated equilibrium structure on a time scale of 3 ps, which is extracted from the down-chirp in the molecular vibrational frequency. When kicked with excess energy of 4 eV, the Ar cage breaks with 50% probability, and the molecule dissociates. The kinetics of polarization selective, multiphoton dissociation with Gaussian laser intensity profiles is delineated and the ballistics of cage breakout is described: The photodissociation proceeds by destruction of the local lattice, by creating interstitials and vacancies. During large amplitude motion on cage-bound potentials, sudden, nonadiabatic spin–flip transitions can be observed and quantified in space and time. The spin–flip occurs with unit probability in Ar when the I*–I bond is stretched beyond 6 Å.
Nanoscale analysis of the In and N spatial redistributions upon annealing of GaInNAs quantum wells
Authors: Chauveau J.-M. , Trampert A. , Ploog K. H. , Tournié E.
Published: April 2004

By using transmission electron microscopy on as-grown and annealed GaInNAs/GaAs heterostructures, we demonstrate that annealing induces a correlated behavior of both In and N species within the GaInNAs quantum well. While no intermixing occurs, the analysis of the strain situation reveals that the main driving force for the observed inward diffusion is not composition gradients at the interfaces, but local strain fields. This mechanism leads to the improvement of the photoluminescence (PL) properties and to the blueshift of the PL peak.
Rate-promoting vibrations and coupled hydrogen–electron transfer reactions in the condensed phase: A model for enzymatic catalysis
Authors: Mincer Joshua S. , Schwartz Steven D.
Published: April 2004

A model is presented for coupled hydrogen–electron transfer reactions in condensed phase in the presence of a rate promoting vibration. Large kinetic isotope effects (KIEs) are found when the hydrogen is substituted with deuterium. While these KIEs are essentially temperature independent, reaction rates do exhibit temperature dependence. These findings agree with recent experimental data for various enzyme-catalyzed reactions, such as the amine dehydrogenases and soybean lipoxygenase. Consistent with earlier results, turning off the promoting vibration results in an increased KIE. Increasing the barrier height increases the KIE, while increasing the rate of electron transfer decreases it. These results are discussed in light of other views of vibrationally enhanced tunneling in enzymes.
Electron transfer in proteins: Nonorthogonal projections onto donor–acceptor subspace of the Hilbert space
Authors: de Andrade Paulo C. P. , Freire José A.
Published: April 2004

We develop nonorthogonal projectors, called Löwdin projectors, to construct an effective donor–acceptor system composed of localized donor (D) and acceptor (A) states of a long-distance electron transfer problem. When these states have a nonvanishing overlap with the bridge states these projectors are non-Hermitian and there are various possible effective two-level systems that can be built. We show how these can be constructed directly from the Schrödinger or Dyson equation projected onto the D–A subspace of the Hilbert space and explore these equations to determine the connection between Hamiltonian and Green function partitioning. We illustrate the use of these effective two-level systems in estimating the electron transfer rate in the context of a simple electron transfer model.
Highly efficient sensitizing of erbium ion luminescence in size-controlled nanocrystalline Si/SiO2 superlattice structures
Authors: Timoshenko V. Yu. , Lisachenko M. G. , Kamenev B. V. , Shalygina O. A. , Kashkarov P. K. , Heitmann J. , Schmidt M. , Zacharias M.
Published: April 2004

Comparative studies of photoluminescence (PL) of undoped and Er-doped size-controlled nanocrystalline Si/SiO2 superlattice structures show that the optical excitation of Si nanocrystals can be completely transferred to the Er3+ ions in surrounding SiO2, resulting in a strong PL line at 1.5 μm. The PL yield of the Er-doped structure increases for higher photon energy of excitation and for smaller nanocrystal sizes. This highly efficient sensitizing of the Er-related PL is explained by a strong coupling between excitons confined in Si nanocrystals and neighboring Er3+ ions in their upper excited states.
Nanostructures and carrier localization behaviors of green-luminescence InGaN/GaN quantum-well structures of various silicon-doping conditions
Authors: Cheng Yung-Chen , Lin En-Chiang , Wu Cheng-Ming , Yang C. C. , Yang Jer-Ren , Rosenauer Andreas , Ma Kung-Jen , Shi Shih-Chen , Chen L. C. , Pan Chang-Chi , Chyi Jen-Inn
Published: April 2004

The results of photoluminescence (PL), detection-energy-dependent photoluminescence excitation (DEDPLE), excitation-energy-dependent photoluminescence (EEDPL), and strain state analysis (SSA) of three InGaN/GaN quantum-well (QW) samples with silicon doping in the well, barrier and an undoped structure are compared. The SSA images show strongly clustering nanostructures in the barrier-doped sample and relatively weaker composition fluctuations in the undoped and well-doped samples. Differences in silicon doping between the samples give rise to the differences in DEDPLE and EEDPL spectra, as a result of the differences in carrier localization. In addition, the PL results provide us clues for speculating that the S-shaped PL peak position behavior is dominated by the quantum-confined Stark effect in an undoped InGaN/GaN QW structure.
Lithography-modulated self-assembly of small ferroelectric Pb(Zr,Ti)O3 single crystals
Authors: Bühlmann S. , Muralt P. , Von Allmen S.
Published: April 2004

Triangular (111) and square-shaped (100) Pb(Zr,Ti)O3 single crystallites with lateral dimensions down to 50 nm and thickness of 20 nm have been grown using lithography-modulated self-assembly in an in situ sputter process. Epitaxial (111)-oriented Pt on a SrTiO3 single crystal served as the substrate. An epitaxial 2 nm thick rutile TiO2 film was grown and patterned into 100–200 nm wide attachment sites by electron beam lithography. The perovskite nucleation density was 60 times higher on TiO2 seeds than on bare Pt(111).
Low-resistance tunnel junctions on GaAs substrates using GaInNAs
Authors: Mars D. E. , Chang Y.-L. , Leary M. H. , Roh S. D. , Chamberlin D. R.
Published: April 2004

Using molecular-beam epitaxy, we have fabricated p-n tunnel junctions lattice matched to GaAs substrates that consist of highly C-doped Ga0.93In0.07As on the p side, and highly Si-doped Ga0.93In0.07N0.02As0.98 on the n side. The introduction of N on the n side of the tunnel junction: (1) lowers the conduction band edge while leaving the valence band edge unchanged, (2) allows the introduction of In to further lower the band gap while remaining lattice matched to GaAs, and (3) increases the maximum Si donor activation that can be achieved. All three of these effects increase the tunneling probability for carriers across the junction and decrease the specific resistance. We estimate the active C acceptors on the p side to be 1.5×1020 cm−3 and the active Si donors on the n side to be 1.8×1019 cm−3. Because of the mutual passivation effect between N and Si atoms, the Si doping level was increased to 1.0×1020 cm−3 to achieve this active net donor concentration. The specific resistance of test tunnel junctions has been measured to be <1×10−5 Ω cm2 corresponding to <0.1 V drop at a current density of 10 kA/cm2. These results are a substantial improvement over corresponding test structures without N on the n side of the junction. The experimental results are in good agreement with model calculations.
Spatial distribution and electronic state of Co in epitaxial anatase CoxTi1−xO2 thin films grown by reactive sputtering
Authors: Jeong B.-S. , Heo Y. W. , Norton D. P. , Kelly J. G. , Rairigh R. , Hebard A. F. , Budai J. D. , Park Y. D.
Published: April 2004

The magnetic and phase properties of CoxTi1−xO2 anatase thin films grown epitaxially on (001) LaAlO3 by a reactive rf magnetron cosputter deposition have been examined. CoxTi1−xO2 (x=0.07) thin films exhibit room-temperature ferromagnetism, as evidenced by hysteresis in M–H loop. Chemical mapping indicates segregation of the Co dopant atoms in these films. However, x-ray photoelectron spectroscopy suggests that the segregated Co is not metallic, but in the Co+2 state. These results are consistent with a segregated Ti–Co–O phase being responsible for the ferromagnetic behavior.
Continuous-wave operation of terahertz quantum-cascade lasers above liquid-nitrogen temperature
Authors: Kumar Sushil , Williams Benjamin S. , Kohen Stephen , Hu Qing , Reno John L.
Published: April 2004

We report cw operation of a quantum-cascade laser at 3.2 THz (λ≈94 μm) up to a heat-sink temperature of 93 K. Resonant longitudinal-optical phonon scattering is used to depopulate the lower radiative state and a low-loss metal–metal waveguide is used to provide high modal confinement. Optical powers of ∼1.8 mW at 10 K and ∼400 μW at 78 K are observed from a single facet of a 40-μm-wide and 1.35-mm-long laser device. A threshold current density of 432 A/cm2 at 10 K and 552 A/cm2 at 78 K was obtained in cw mode. The same device lased up to 129 K in pulsed mode with a threshold current density of 419 A/cm2 at 5 K.
Self-assembly of carbon nanohelices: Characteristics and field electron emission properties
Authors: Zhang Guangyu , Jiang Xin , Wang Enge
Published: April 2004

We report the synthesis of self-assembled carbon nanohelices on iron needles using microwave plasma assisted chemical vapor deposition. The catalytic growth can be explained by the vapor–liquid–solid theory. Their morphologies and microstructures are investigated by scanning electron microscopy, high-resolution transmission electron microscopy, nanobeam diffraction, and Raman spectroscopy. The field-emission investigations show a rather low turn-on electrical field and high emission current.
Carbon nanotubes-zeolite complex: A Li-intercalated compound with high storage capacity
Authors: Liu H. J. , Li Z. M. , Liang Q. , Tang Z. K. , Chan C. T.
Published: April 2004

We report a composite system for Li intercalation, in which ultrasmall-diameter (4 Å) carbon nanotubes are confined inside the channels of nanoporous zeolite crystals. The first-principles pseudopotential calculations show that there are several possible sites for lithium to be intercalated, including the interior and exterior of the nanotubes. The vapor phase adsorption and electrochemical measurements both indicate that the lithium capacity of the system can be ∼10% by weight, which is higher than that of graphite intercalation compounds. The enhanced Li capacity makes the nanotubes-zeolite complex a plausible candidate for Li battery applications.
Finite element modeling of piezoresponse in nanostructured ferroelectric films
Authors: Li J.-H. , Chen L. , Nagarajan V. , Ramesh R. , Roytburd A. L.
Published: April 2004

Patterning thin ferroelectric films into discrete islands is an effective way to release the constraint imposed by a substrate and the unpoled nonpiezoactive surrounding film to enhance the film piezoresponse. The converse piezoresponse measured by the surface displacement of ferroelectric islands, with lateral size changing from a nanoscale to a continuous film, has been modeled using three-dimensional finite element method. The modeling has shown that piezodeformation of the islands results in a local deformation of a substrate in the vicinity of island. The deformation is larger when the substrate is softer. The deformation, together with clamping strain in the film, decreases the effective d33 of the film island. The effect of the top electrode on d33 measured by surface displacement is also modeled. The piezoresponse of different size island capacitors with PbZr0.5Ti0.5O3/SrTiO3/Si and PbZr0.2Ti0.8O3/SrTiO3 heterostructures has been calculated. The results of modeling are in good agreement with experimental data on d33 obtained by piezoresponse force microscopy.
Thin-film heterostructure solid oxide fuel cells
Authors: Chen X. , Wu N. J. , Smith L. , Ignatiev A.
Published: April 2004

A micro thin-film solid oxide fuel cell (TFSOFC) has been designed based on thin-film deposition and microlithographic processes. The TFSOFC is composed of a thin-film electrolyte grown on a nickel foil substrate and a thin-film cathode deposited on the electrolyte. The Ni foil substrate is then processed into a porous anode by photolithographic patterning and etching to develop pores for gas transport into the fuel cell. A La0.5Sr0.5CoO3 (LSCO) thin-film cathode is then deposited on the electrolyte, and a porous NiO–YSZ cermet layer is added to the anode to improve the electrode performance. The TFSOFC has stably operated in a temperature ranges as low as 480–570 °C, significantly lower than bulk SOFC’s, and has yielded a maximum output power density of ∼110 mW/cm2 in that temperature range.
Influence of Al doping on lattice strain and electrical properties of epitaxial GaN films grown by metalorganic chemical vapor deposition on Al2O3 substrate
Authors: Jeong Jae Kyeong , Choi Jung-Hae , Hwang Cheol Seong , Kim Hyeong Joon , Lee Jae-Hoon , Lee Jung-Hee , Kim Chang-Soo
Published: April 2004

The effects of the isoelectronic Al doping of epitaxial GaN films grown by metalorganic chemical vapor deposition on a (0001) Al2O3 single crystal substrate were investigated. It was found that the threading screw and edge dislocation densities of the GaN film decreased to less than half of that of the undoped GaN film up to Al doping concentration of 0.45%. The in-plane and out-of-plane strains were simultaneously reduced with the decrease in dislocation density as a result of the solution hardening effect. Accordingly, the electron mobility of the 0.45% Al-doped GaN film (524 cm2/Vs) was greatly improved compared to that of the undoped GaN film (178 cm2/Vs). However, the threading dislocation densities and strains were increased at a 0.64% Al concentration, and the electron mobility decreased accordingly. Therefore, the improvement in the electron mobility by Al doping up to 0.45% is the result of a decrease in the threading dislocation density and not a decrease in the number of point defects (Ga-site vacancy) as suggested earlier [Lee et al., Appl. Phys. Lett. 83, 917 (2003)].
Forced polarization of α-sapphire induced by coated LiNbO3 and LiTaO3 films
Authors: Yang X. , Wu X. L. , Feng Y. , Li J. , Jiang M.
Published: April 2004

We have investigated the formation mechanism of the interfacial electric field in LiNbO3(or LiTaO3)/α-sapphire crystal structures, which is important in understanding the photoluminescence properties of this kind of ferroelectric film-coated crystal material. It is revealed that the interfacial electric field arises from the interfacial polarization charge generated during poling of LiNbO3(or LiTaO3) film near Curie temperature, which induces forced polarization of the α-sapphire crystal. As a result, lattice distortions of the α-sapphire crystal change the crystal field of Cr3+ ion in the sapphire crystal and therefore lead to intensity enhancement of R-line luminescence from Cr3+ centers.
Modification of GaN(0001) growth kinetics by Mg doping
Authors: Monroy E. , Andreev T. , Holliger P. , Bellet-Amalric E. , Shibata T. , Tanaka M. , Daudin B.
Published: April 2004

We have studied the effect of Mg doping on the surface kinetics of GaN during growth by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface of GaN, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN. The growth window is hence significantly reduced. Higher growth temperatures lead to an enhancement of Mg segregation and an improvement of the surface morphology.
Inelastic tunneling spectroscopy using scanning tunneling microscopy on trans-2-butene molecule: Spectroscopy and mapping of vibrational feature
Authors: Sainoo Y. , Kim Y. , Komeda T. , Kawai Maki
Published: April 2004

Inelastic tunneling spectroscopy (IETS) measurement using scanning tunneling microscopy (STM) with a commercially available STM set up is presented. The STM–IETS spectrum measured on an isolated trans-2-butene molecule on the Pd(110) shows a clear vibrational feature in d2I/dV2 at the bias voltage of 360 mV and −363 mV, which corresponds to the ν(C-H) mode (d2I/dV2∼10 nA/V2). In addition, we have obtained an image by mapping the vibrational feature of ν(C-H) in d2I/dV2. The image is obtained by scanning the tip on the surface with the feedback loop activated while the modulation voltage is superimposed on the sample voltage. With the method that is readily performable with conventional software, we have clearly differentiated the molecules of trans-2-butene and butadiene through the mapping of the vibrational feature, demonstrating its capability of chemical identification in atomic scale.
Increased Stability of NO and NS Heterocyclic Carbenes?
Authors: Graham David C. , Yates Brian F.
Published: April 2004

Density functional theory has been used to investigate the effects of alkylation and oxidation on the stability of NO and NS heterocyclic carbenes. While O- and S-alkylation leads to a dramatic increase in stability with respect to dimerization, oxidation of the NS heterocyclic carbene to form the sulphoxide appears to have the opposite effect.
Fructose-Permeable Liquid Membranes Containing Boronic Acid Carriers
Authors: Duggan Peter J.
Published: April 2004

Liquid membranes that contain boronic acids have potential application in environmentally benign industrial D-fructose production. This review describes our efforts to develop boronic acid carriers that promote high fluxes, that are resistant to leaching, and that are highly selective for fructose over other sugars. Considerable progress has been made with multidentate boronic acid carriers. Initial attempts to transport D-fructose as macrocyclic β-D-fructopyranose diesters appeared to suffer from competitive transport of macrocyclic α-D-glucofuranose diesters, and did not lead to high D-fructose selectivity. On the other hand, carriers that can bind multiple equivalents of D-fructose as tridentate β-D-fructofuranose esters have been much more effective. Unfortunately, D-fructose selectivity is still apparently limited by a competitive and boronic acid-independent non-selective ‘mobile fixed site relay’ transport process. However, further progress will be possible through improved carrier design, careful investigation of the various stages of the transport process, and the use of more industrially useful membrane configurations.
The Fluorination (at C5) of Some Derivatives of D-Glucose
Authors: Skelton Brian W. , Stick Robert V. , Stubbs Keith A. , Watts Andrew G. , White Allan H.
Published: April 2004

The photobromination of various per-esters of β-D-glucopyranose and α- and β-D-glucopyranosyl fluoride has yielded 5-bromo derivatives capable of conversion into the corresponding 5-fluorides. The best reagent for this conversion was found to be silver tetrafluoroborate in ether/dichloromethane. The single-crystal X-ray structure determination of penta-O-benzoyl-5-fluoro-α-L-idopyranose is presented.As well, various approaches to 5-fluoro glycopyranosides have been developed. The photobromination of phenyl tetra-O-acetyl-β-D-glucopyranoside, followed by fluorination and protecting group removal gave phenyl 5-fluoro-β-D-glucopyranoside. The photobromination of penta-O-acetyl-β-D-glucopyranose, followed by hydro- lysis and treatment with methanol, gave a hemiacetal that was converted via treatment with diethylaminosulfur trifluoride followed by protecting group removal into methyl 5-fluoro-β-D-glucopyranoside. Methyl 2,3,4-tri-O-benzyl-6-deoxy-α- and -β-D-xylo-hex-5-enosides were converted into their corresponding epoxides with either dimethyldioxirane or 3-chloroperbenzoic acid; subsequent treatment with hydrogen fluoride/pyridine then generated the 5-fluoro glycopyranosides as the major products. A single-crystal X-ray structure determination of 1,6-anhydro-2,3,4-tri-O-benzyl-5-hydroxy-β-L-idose is presented.
Loss of Symbiodinium from bleached Australian scleractinian corals (Acropora
hyacinthus, Favites complanata and Porites solida)
Authors: Strychar Kevin B. , Coates Mike , Sammarco Paul W.
Published: April 2004

Coral bleaching results from the dissociation of Symbiodinium and is primarily related to sea surface temperatures above mean yearly maximums. The numbers of live, dead, and mitotic Symbiodinium cells lost from three scleractinian corals from three different families (Acropora hyacinthus, Favites complanata, and Porites solida), which have not been studied previously in central Queensland (Australia), were compared at 28, 30, 32, and 34°C. Specific expulsion rates, growth rates, and mitotic indices were compared for each host at each temperature. Porites solida was the most robust coral, A. hyacinthus bleached more readily at low temperatures and F. complanata showed levels of intermediate bleaching tolerance to elevated temperatures. However, the timing of Symbiodinium cell loss was similar between all corals tested. Mitotic indices and specific growth rates were found to be positively associated with increasing temperature; thus, symbiont reproduction increased despite elevated losses of Symbiodinium from the host. Because all corals in the present study were symbiotic with Symbiodinium from clade C, different levels of stress tolerance to temperature suggests that bleaching resistance is an attribute associated with the coral host and, to a lesser degree, the symbiont.
Estimating the contribution of sympatric anadromous and freshwater resident brown trout to juvenile production
Authors: Charles K. , Roussel J.-M. , Cunjak R. A.
Published: April 2004

Carbon and nitrogen stable isotope analysis was used to study the reproductive contributions of anadromous and freshwater resident female brown trout (Salmo trutta L.) in La Roche Brook (Normandy, France), where both forms live in sympatry. Sixty-nine emerging fry were sampled by electrofishing in three different locations in the lower, middle and upper reaches of the stream, in March–April 2002. A collection of samples with known origin (brown trout eggs and fin tissues and benthic invertebrates) allowed classification of each emerging fry as the progeny of freshwater resident (δ13C = –26.0‰ ± 0.8 s.d.; δ15N = 12.5‰ ± 1.4 s.d.) or anadromous (δ13C = –18.8‰ ± 0.6 s.d., δ15N = 14.8‰ ± 0.9 s.d.) female brown trout. It was then possible to estimate the relative contribution (33%) of anadromous females to the population of fry that emerged from redds in 2002 and to evaluate the extent to which freshwater and anadromous spawning grounds overlapped in the stream.
Expression of plant protein phosphatase 2C interferes with nuclear import of the
Agrobacterium
T-complex protein VirD2
Authors: Tao Yumin , Rao Praveen K. , Bhattacharjee Saikat , Gelvin Stanton B.
Published: March 2004

Agrobacterium tumefaciens
transfers DNA to plant cells as a single-stranded DNA molecule (the T-strand) covalently linked to VirD2 protein. VirD2 contains nuclear localization signal sequences that presumably help direct the T-strand to the plant nucleus. We identified a tomato cDNA clone, DIG3, that encodes a protein that interacts with the C-terminal region of VirD2. DIG3 encodes an enzymatically active type 2C serine/threonine protein phosphatase. Overexpression of DIG3 in tobacco BY-2 protoplasts inhibited nuclear import of a β-glucuronidase-VirD2 nuclear localization signal fusion protein. Thus, DIG3 may be involved in nuclear import of the VirD2 protein and, consequently, the VirD2/transferred DNA complex.
On the sharpness of the interfaces in metallic multilayers
Authors: Holmström E. , Nordström L. , Bergqvist L. , Skubic B. , Hjörvarsson B. , Abrikosov I. A. , Svedlindh P. , Eriksson O.
Published: March 2004

We show that the three most relevant magnetic properties (magnetic moment, critical temperature, and interlayer exchange coupling) of metallic multilayers can be reproduced with good accuracy by first principles theory, provided that the picture of atomically sharp interfaces is abandoned and one allows instead for both interface alloying and interface roughness. The interface of a metallic multilayer (exemplified by the Fe/V system) is demonstrated to, at best, have interdiffusion essentially over two to three atomic layers on each side of the interface. Our conclusions are the result of combining experimental work with theoretical modeling, and we argue that this approach is the best avenue to obtain accurate information about the interface quality of metallic multilayers.
Classification of natural textures in echolocation
Authors: Grunwald Jan-Eric , Schörnich Sven , Wiegrebe Lutz
Published: April 2004

Through echolocation, a bat can perceive not only the position of an object in the dark; it can also recognize its 3D structure. A tree, however, is a very complex object; it has thousands of reflective surfaces that result in a chaotic acoustic image of the tree. Technically, the acoustic image of an object is its impulse response (IR), i.e., the sum of the reflections recorded when the object is ensonified with an acoustic impulse. The extraction of the acoustic IR from the ultrasonic echo and the detailed IR analysis underlies the bats' extraordinary object-recognition capabilities. Here, a phantom-object playback experiment is developed to demonstrate that the bat
Phyllostomus discolor
can evaluate a statistical property of chaotic IRs, the IR roughness. The IRs of the phantom objects consisted of up to 4,000 stochastically distributed reflections. It is shown that
P. discolor
spontaneously classifies echoes generated with these IRs according to IR roughness. This capability enables the bats to evaluate complex natural textures, such as foliage types, in a meaningful manner. The present behavioral results and their simulations in a computer model of the bats' ascending auditory system indicate the involvement of modulation-sensitive neurons in echo analysis.
Akt plays a central role in sarcomagenesis induced by Kaposi's sarcoma herpesvirus-encoded G protein-coupled receptor
Authors: Sodhi Akrit , Montaner Silvia , Patel Vyomesh , Gómez-Román José Javier , Li Yi , Sausville Edward A. , Sawai Earl T. , Gutkind J. Silvio
Published: March 2004

We have recently engineered an
in vivo
endothelial cell-specific retroviral gene transfer system and found that a single Kaposi's sarcoma (KS)-associated herpesvirus/human herpesvirus 8 gene encoding a G protein-coupled receptor (vGPCR), is sufficient to induce KS-like tumors in mice. By using this system, we show here that the Akt signaling pathway plays a central role in vGPCR oncogenesis. Indeed, a constitutively active Akt was sufficient to induce benign hemangiomas in mice, whereas heterozyogosity for PTEN (the phosphatase and tension homologue deleted on chromosome 10), modestly enhancing basal Akt activity, dramatically enhanced vGPCR sarcomagenesis. Examination of KS biopsies from AIDS patients revealed active Akt as a prominent feature, supportive of a role for Akt in human Kaposi's sarcomagenesis. By using a vGPCR agonist-dependent mutant, we further establish constitutive activity as a requirement for vGPCR sarcomagenesis, validating targeted inhibition of key vGPCR signaling pathways as an approach for preventing its oncogenic potential. These observations prompted us to explore the efficacy of inhibiting Akt activation as a molecular approach to KS treatment. Pharmacological inhibition of the Akt pathway with the chemotherapeutic agent 7-hydroxystaurosporine prevented proliferation of vGPCR-expressing endothelial cells
in vitro
and inhibited their tumorigenic potential
in vivo
. Both were associated with a decrease in Akt activity. These results identify Akt as an essential player in vGPCR sarcomagenesis and demonstrate the therapeutic potential of drugs targeting this pathway in the treatment of KS.
Gene discovery in genetically labeled single dopaminergic neurons of the retina
Authors: Gustincich Stefano , Contini Massimo , Gariboldi Manuela , Puopolo Michelino , Kadota Koji , Bono Hidemasa , LeMieux Julianna , Walsh Pamela , Carninci Piero , Hayashizaki Yoshihide , Okazaki Yasushi , Raviola Elio
Published: March 2004

In the retina, dopamine plays a central role in neural adaptation to light. Progress in the study of dopaminergic amacrine (DA) cells has been limited because they are very few (450 in each mouse retina, 0.005% of retinal neurons). Here, we applied transgenic technology, single-cell global mRNA amplification, and cDNA microarray screening to identify transcripts present in DA cells. To profile gene expression in single neurons, we developed a method (SMART7) that combines a PCR-based initital step (switching mechanism at the 5′ end of the RNA transcript or SMART) with T7 RNA polymerase amplification. Single-cell targets were synthesized from genetically labeled DA cells to screen the RIKEN 19k mouse cDNA microarrays. Seven hundred ninety-five transcripts were identified in DA cells at a high level of confidence, and expression of the most interesting genes was confirmed by immunocytochemistry. Twenty-one previously undescribed proteins were found in DA cells, including a chloride channel, receptors and other membrane glycoproteins, kinases, transcription factors, and secreted neuroactive molecules. Thirty-eight percent of transcripts were ESTs or coding for hypothetical proteins, suggesting that a large portion of the DA cell proteome is still uncharacterized. Because cryptochrome-1 mRNA was found in DA cells, immunocytochemistry was extended to other components of the circadian clock machinery. This analysis showed that DA cells contain the most common clock-related proteins.