bluuebunny/crossref_metadata_2025 huggingface dataset:
Locomotor effects of imidazoline I2‐site‐specific ligands and monoamine oxidase inhibitors in rats with a unilateral 6‐hydroxydopamine lesion of the nigrostriatal pathway
Authors: MacInnes Nicholas , Duty Susan
Published: November 2004

The present study examined the ability of the selective imidazoline I2‐site ligands 2‐(‐2‐benzofuranyl)‐2‐imidazoline (2‐BFI) and 2‐[4,5‐dihydroimidaz‐2‐yl]‐quinoline (BU224) and selected monoamine oxidase (MAO) inhibitors to evoke locomotor activity in rats bearing a lesion of the nigrostriatal pathway.

Male Sprague–Dawley rats were injected with 12.5 μg 6‐hydroxydopamine (6‐OHDA) into the right median forebrain bundle to induce a unilateral lesion of the nigrostriatal tract. After 6 weeks, test drugs were administered either alone or in combination with L‐DOPA (L‐3,4‐dihydroxyphenylamine) and the circling behaviour of animals was monitored as an index of anti‐Parkinsonian activity.

Intraperitoneal (i.p.) administration of the irreversible MAO‐B inhibitor deprenyl (20 mg kg−1) or the imidazoline I2‐site ligands BU224 (14 mg kg−1) and 2‐BFI (7 and 14 mg kg−1) produced significant increases in ipsiversive rotations compared to vehicle controls totaling, at the highest respective doses tested, 521±120, 131±37 and 92.5±16.3 net contraversive rotations in 30 (deprenyl) or 60 (BU224 and 2‐BFI) min. In contrast, the reversible MAO‐A inhibitor moclobemide (2.5–10 mg kg−1) and the reversible MAO‐B inhibitor lazabemide (2.5–10 mg kg−1) failed to instigate significant rotational behaviour compared to vehicle.

Coadministration of lazabemide (10 mg kg−1), moclobemide (10 mg kg−1) or 2‐BFI (14 mg kg−1) with L‐DOPA (20 mg kg−1) significantly increased either the duration or total number of contraversive rotations emitted over the testing period in comparison to L‐DOPA alone.

These data suggest that I2‐specific ligands have dual effects in the 6‐OHDA‐lesioned rat model of Parkinson's disease; a first effect associated with an increase in activity in the intact hemisphere, probably via an increase in striatal dopamine content, and a secondary action which, through the previously documented inhibition of MAO‐A and/or MAO‐B, increases the availability of dopamine produced by L‐DOPA.

British Journal of Pharmacology (2004) 143, 952–959. doi:10.1038/sj.bjp.0706019
Bradykinin specificity and signaling at GPR100 and B2 kinin receptors
Authors: Fredrik Leeb‐Lundberg L M
Published: November 2004

British Journal of Pharmacology (2004) 143, 931–932. doi:10.1038/sj.bjp.0706031
High-order averaging schemes with error bounds for thermodynamical properties calculations by molecular dynamics simulations
Authors: Cancès Eric , Castella François , Chartier Philippe , Faou Erwan , Le Bris Claude , Legoll Frédéric , Turinici Gabriel
Published: November 2004

We introduce high-order formulas for the computation of statistical averages based on the long-time simulation of molecular dynamics trajectories. In some cases, this allows us to significantly improve the convergence rate of time averages toward ensemble averages. We provide some numerical examples that show the efficiency of our scheme. When trajectories are approximated using symplectic integration schemes (such as velocity Verlet), we give some error bounds that allow one to fix the parameters of the computation in order to reach a given desired accuracy in the most efficient manner.
Hydrogen storage in LiAlH4: Predictions of the crystal structures and reaction mechanisms of intermediate phases from quantum mechanics
Authors: Kang Jeung Ku , Lee Jai Young , Muller Richard P. , Goddard William A.
Published: November 2004

We use the density functional theory and x-ray and neutron diffraction to investigate the crystal structures and reaction mechanisms of intermediate phases likely to be involved in decomposition of the potential hydrogen storage material LiAlH4. First, we explore the decomposition mechanism of monoclinic LiAlH4 into monoclinic Li3AlH6 plus face-centered cubic (fcc) Al and hydrogen. We find that this reaction proceeds through a five-step mechanism with an overall activation barrier of 36.9 kcal/mol. The simulated x ray and neutron diffraction patterns from LiAlH4 and Li3AlH6 agree well with experimental data. On the other hand, the alternative decomposition of LiAlH4 into LiAlH2 plus H2 is predicted to be unstable with respect to that through Li3AlH6. Next, we investigate thermal decomposition of Li3AlH6 into fcc LiH plus Al and hydrogen, occurring through a four-step mechanism with an activation barrier of 17.4 kcal/mol for the rate-limiting step. In the first and second steps, two Li atoms accept two H atoms from AlH6 to form the stable Li-H-Li-H complex. Then, two sequential H2 desorption steps are followed, which eventually result in fcc LiH plus fcc Al and hydrogen: Li3AlH6(monoclinic)→3 LiH(fcc)+Al(fcc)+3/2 H2 is endothermic by 15.8 kcal/mol. The dissociation energy of 15.8 kcal/mol per formula unit compares to experimental enthalpies in the range of 9.8–23.9 kcal/mol. Finally, we explore thermal decomposition of LiH, LiH(s)+Al(s)→LiAl(s)+12H2(g) is endothermic by 4.6 kcal/mol. The B32 phase, which we predict as the lowest energy structure for LiAl, shows covalent bond characters in the Al-Al direction. Additionally, we determine that transformation of LiH plus Al into LiAlH is unstable with respect to transformation of LiH through LiAl.
Energy band dispersion in well ordered N,N′-dimethyl-3,4,9,10-perylenetetracarboxylic diimide films
Authors: Gavrila G. N. , Mendez H. , Kampen T. U. , Zahn D. R. T. , Vyalikh D. V. , Braun W.
Published: November 2004

The electronic properties of well ordered N,N′-dimethyl-3,4,9,10-perylenetetracarboxylic dimide (DiMe-PTCDI) films prepared on sulfur passivated GaAs(001) substrates were studied by means of photoemission spectroscopy. From the photon energy dependence of normal emission spectra an intermolecular energy band dispersion of about 0.2eV was determined for the highest occupied molecular orbital (HOMO). Simulation of the density of states reveals that the HOMO band has a single π -character. The observed energy band dispersion thus originates from the intermolecular π-π interaction and is modeled using the tight binding model. The analysis provides a value of 0.04eV for the transfer integral. The inner potential was treated as a fitting parameter such that the expected periodicity of the dispersion in the reciprocal space was obtained.
Dynamical and structural properties of benzene in supercritical water
Authors: Nieto-Draghi Carlos , Bonet Àvalos Josep , Contreras Oliver , Ungerer Philippe , Ridard Jacqueline
Published: November 2004

We have employed an anisotropic united atom model of benzene (R. O. Contreras, Ph.D. thesis, Universitat Rovira i Virgili 2002) that reproduces the quadrupolar moment of this molecule through the inclusion of seven point charges. We show that this kind of interaction is required to reproduce the solvation of these molecules in supercritical water. We have computed self-diffusion coefficient and Maxwell-Stefan coefficients as well as the shear viscosity for the mixture water-benzene at supercritical conditions. A strong density and composition dependence of these properties is observed. In addition, our simulations are in qualitative agreement with the experimental evidence that, at medium densities (0.6 g/cm3 and 673 K), almost half of the benzene molecules have one hydrogen bond with water molecules. We also observe that these bonds are longer lived than the corresponding hydrogen bonds between water molecules. Similarly, we obtain an important reduction of the dielectric constant of the mixture with the increment of the amount of benzene molecules at medium and high densities.
Theoretical study of the electronic structure of CnS (n=1–6) thiocumulenes
Authors: Pérez-Juste Ignacio , Graña Ana M. , Carballeira Luis , Mosquera Ricardo A.
Published: November 2004

Linear sulfur-carbon chains CnS (n=1–6) of astronomical interest were examined by means of several theoretical methods. The three smallest compounds of the series were chosen to evaluate the performance of several computational models, including Hartree–Fock theory, density functional theory with the Becke’s three parameter exchange functional and the correlation functional of Lee, Yang, and Parr (B3LYP), and electron-correlated methods (second-order Møller-Plesset perturbation method (MP2), configuration interaction method including single and double excitations (CISD), and quadratic configuration interaction method including single and double excitations (QCISD) in combination with a large variety of basis sets. The systematic comparison between the experiment and theory indicates that the B3LYP/6-311G** method can be considered suitable for the study of the electronic structures of the CnS compounds. The electronic ground states of the CnS molecules alternate between Σ1 and Σ3 for odd and even values of n, respectively. The B3LYP/6-311G** wave functions for these electronic ground states were analyzed by means of the atoms in molecules (AIM) and natural bond orbital (NBO) methods. Both approaches suggest that the electronic structures for the singlet and triplet compounds must be considered separately. According to the NBO method, singlet compounds can be properly represented by acetylenic structures with alternating single and triple bonds (S≡C–C≡C…). However, triplet compounds are better described by means of double bond-double bond cumulenic structures (S=C=C=C=C…) as a consequence of the average between different α and β electronic densities. AIM delocalization indexes and NBO interactions between localized orbitals also indicate that these structures are strongly π delocalized. Finally, the different singlet and triplet structures proposed provide a consistent explanation for the geometries, dipole moments, and spin-density values of the CnS compounds studied.
Nanospheres in phase-separating multicomponent fluids: A three-dimensional dissipative particle dynamics simulation
Authors: Laradji Mohamed , Hore Michael J. A.
Published: November 2004

The dynamics of phase separation of three-dimensional fluids containing nanospheres, which interact preferentially with one of the two fluids, is studied by means of large-scale dissipative particle dynamics simulations. We systematically investigated the effect of volume fraction, radius, and mass of the nanoparticles on both kinetics and morphology of the binary mixture. We found that nanospheres lead to a reduction of domain growth which is intensified as their volume fraction is increased for a given radius of nanoparticles, or as the nanoparticles radius is decreased for a given volume fraction. Up to moderate volume fractions of nanoparticles, the growth law, however, is found to be identical to that pure binary fluids, i.e., R(t)∼tn, with n=1. For relatively high volume fractions of nanoparticles, a diffusive growth regime was detected. The crossover to the slower growth regime as the nanoparticles volume fraction is increased or their radius is decreased is associated with the crystallization of the nanospheres within the preferred component. These results are qualitatively in good agreement with previous two-dimensional simulations using molecular dynamics [M. Laradji and G. MacNevin, J. Chem. Phys. 119, 2275 (2003)] and a time-dependent Ginzburg-Landau model [M. Laradji, J. Chem. Phys. 120, 9330 (2004)], as well as recent experiments.
A multichannel electron energy loss spectrometer for low-temperature condensed films
Authors: David Donald E. , Popović Duška B. , Antic Dean , Michl Josef
Published: November 2004

We describe a wide-gap multichannel cylindrical deflection electron energy analyzer suitable for measuring the weak signals characteristic of electronically inelastic electron energy loss spectra. The analyzer has nearly ideal fringing field termination, and its resolution and energy dispersion were characterized as a function of energy by solving numerically the equation of motion of electrons in an ideal cylindrical electric field. The numerical results for the radial location of the electrons at the detector as a function of the entrance location, angle, and energy are closely approximated by a second order polynomial, and match closely with those observed. The detection efficiency of the analyzer is 100–150 times better than that of an equivalent single-channel instrument, but limited energy transmission of the zoom lens system used in our case reduced it by a factor of about 2. The performance of the new instrument was demonstrated by measuring the E1u3 electronic spectrum of benzene in only 2 min and the spectrum of endo-benzotricyclo[4.2.1.02.5]nonane.
Probing electronic coupling in excitonically coupled heterodimer complexes by two-color three-pulse photon echoes
Authors: Mančal Tomáš , Fleming Graham R.
Published: November 2004

Following the earlier work of Yang et al. [J. Chem. Phys. 110 (1999) 2983] analytical expressions for the downhill and uphill resonant two-color three-pulse photon echo peak shift (2C-3PEPS) of a heterodimer system are derived in the impulsive limit. It is shown how to obtain information about coupling between the components of the dimer from the combined one- and two-color peak shift measurements. Further analytical relations are derived which enable site specific information about the environment of the components, including the relative difference of the inhomogeneity and the difference between the energy-gap correlation functions on the heterodimer sites to be obtained. The simulations show only a very small influence of the laser pulse length on the measured values of coupling coefficient and other relevant quantities suggesting that current 2C-3PEPS measurements can find practical application in directly measuring couplings in excitonically coupled heterodimer complexes.
Conformation of a polymer chain in solution: An exact density expansion approach
Authors: Taylor Mark P.
Published: November 2004

The conformation of a polymer chain in solution is intrinsically coupled to the thermodynamic and structural properties of the solvent. Here we study such solvent effects in a system consisting of a flexible interaction-site n-mer chain immersed in a monomeric solvent. Chain conformation is described with a set of intramolecular site-site probability functions. We derive an exact density expansion for these intramolecular probability functions and give a diagrammatic representation of the terms contributing at each order of the expansion. The expansion is tested for a short hard-sphere chain (n=3 or 4) with site diameter σ in a hard-sphere solvent with solvent diameter D. In comparison with Monte Carlo simulation results for 0.2⩽D/σ⩽100, the expansion (taken to second order) is found to be quantitatively accurate for low to moderate solvent volume fractions for all size ratios. Average chain dimensions are predicted accurately up to liquidlike solvent densities. The hard-sphere chains are compressed with both increasing solvent density and decreasing solvent size. For small solvent (D<σ), depletion effects are found and the chain structure is strongly perturbed even at low solvent volume fractions.
Singular structure of magnetic islands resulting from reconnection
Authors: Jemella B. D. , Drake J. F. , Shay M. A.
Published: November 2004

Magnetic island equilibria resulting from reconnection in magnetohydrodynamic (MHD) simulations are explored in a two-dimensional slab geometry. Magnetic islands are evolved to finite amplitude with a nonzero resistivity. The resistivity and flows are then set to zero and the system is allowed to relax toward equilibrium. A y-type singular current layer in the equilibrium state is identified for all but systems with the smallest values of the tearing mode stability parameter Δ′. It is shown that the length of the equilibrium y line tracks the length of the Sweet–Parker current layer that develops during reconnection. This suggests that the formation of Sweet–Parker current layers during magnetic reconnection in the resistive MHD model is a consequence of the presence of a singularity in post-reconnection state. A threshold in Δ′ for singular behavior is also identified.
HREELS, STM, and STS study of CH3-terminated Si(111)-(1×1) surface
Authors: Yamada Taro , Kawai Maki , Wawro Andrzej , Suto Shozo , Kasuya Atsuo
Published: November 2004

An ideally (1×1)-CH3(methyl)-terminated Si(111) surface was composed by Grignard reaction of photochlorinated Si(111) and the surface structure was for the first time confirmed by Auger electron spectroscopy, low energy electron diffraction, high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). HREELS revealed the vibration modes associated to the CH3-group as well as the C-Si bond. STM discerned an adlattice with (1×1) periodicity on Si(111) composed of protrusions with internal features, covering all surface terraces. The surface structure was confirmed to be stable at temperatures below 600 K. STS showed that an occupied-state band exists at gap voltage of −1.57 eV, generated by the surface CH3 adlattice. This CH3:Si(111)-(1×1) adlayer with high stability and unique electronic property is prospective for applications such as nanoscale lithography and advanced electrochemistry.
Single-crystalline tin-doped indium oxide whiskers: Synthesis and characterization
Authors: Wan Q. , Song Z. T. , Feng S. L. , Wang T. H.
Published: November 2004

An in situ doping approach was adopted to synthesize single-crystalline Sn-doped In2O3 [indium tin oxide (ITO)] nanowhiskers. Similar synthesis strategy could be used in the production of various doped metal oxide nanowhiskers. The growth mode of ITO nanowhiskers was discussed based on a self-catalytic vapor–liquid–solid growth mechanism. At room temperature, a photoluminescence peak at 510nm was observed, which was likely related to the surface defects of ITO nanowhiskers. In air ambient, the resistivity of individual ITO whisker was measured to be 0.40Ωcm, which was much higher than that of ITO films. A possible explanation for the high resistivity was proposed based on the influence of surface oxygen absorption.
Viscosity of confined inhomogeneous nonequilibrium fluids
Authors: Zhang Junfang , Todd B. D. , Travis Karl P.
Published: November 2004

We use the nonlocal linear hydrodynamic constitutive model, proposed by Evans and Morriss [Statistical Mechanics of Nonequilibrium Liquids (Academic, London, 1990)], for computing an effective spatially dependent shear viscosity of inhomogeneous nonequilibrium fluids. The model is applied to a simple atomic fluid undergoing planar Poiseuille flow in a confined channel of several atomic diameters width. We compare the spatially dependent viscosity with a local generalization of Newton’s law of viscosity and the Navier–Stokes viscosity, both of which are known to suffer extreme inaccuracies for highly inhomogeneous systems. The nonlocal constitutive model calculates effective position dependent viscosities that are free from the notorious singularities experienced by applying the commonly used local constitutive model. It is simple, general, and has widespread applicability in nanofluidics where experimental measurement of position dependent transport coefficients is currently inaccessible. In principle the method can be used to predict approximate flow profiles of any arbitrary inhomogeneous system. We demonstrate this by predicting the flow profile for a simple fluid undergoing planar Couette flow in a confined channel of several atomic diameters width.
Long-time dynamics of Rouse–Zimm polymers in dilute solutions with hydrodynamic memory
Authors: Lisy V. , Tothova J. , Zatovsky A. V.
Published: November 2004

The dynamics of flexible polymers in dilute solutions is studied taking into account the hydrodynamic memory, as a consequence of fluid inertia. As distinct from the Rouse–Zimm (RZ) theory, the Boussinesq friction force acts on the monomers (beads) instead of the Stokes force, and the motion of the solvent is governed by the nonstationary Navier–Stokes equations. The obtained generalized RZ equation is solved approximately using the preaveraging of the Oseen tensor. It is shown that the time correlation functions describing the polymer motion essentially differ from those in the RZ model. The mean-square displacement (MSD) of the polymer coil is at short times ∼t2 (instead of ∼t). At long times the MSD contains additional (to the Einstein term) contributions, the leading of which is ∼t. The relaxation of the internal normal modes of the polymer differs from the traditional exponential decay. It is displayed in the long-time tails of their correlation functions, the longest lived being ∼t−3/2 in the Rouse limit and t−5/2 in the Zimm case, when the hydrodynamic interaction is strong. It is discussed that the found peculiarities, in particular, an effectively slower diffusion of the polymer coil, should be observable in dynamic scattering experiments.
Replica exchange molecular dynamics simulations of amyloid peptide aggregation
Authors: Cecchini M. , Rao F. , Seeber M. , Caflisch A.
Published: November 2004

The replica exchange molecular dynamics (REMD) approach is applied to four oligomeric peptide systems. At physiologically relevant temperature values REMD samples conformation space and aggregation transitions more efficiently than constant temperature molecular dynamics (CTMD). During the aggregation process the energetic and structural properties are essentially the same in REMD and CTMD. A condensation stage toward disordered aggregates precedes the β-sheet formation. Two order parameters, borrowed from anisotropic fluid analysis, are used to monitor the aggregation process. The order parameters do not depend on the peptide sequence and length and therefore allow to compare the amyloidogenic propensity of different peptides.
Dipole-quadrupole and dipole-octopole polarizability of OsO4 from depolarized collision-induced light scattering experiments, ab initio and density functional theory calculations
Authors: Hohm Uwe , Maroulis G.
Published: November 2004

The dipole-quadrupole and dipole-octopole polarizability of osmium tetroxide (OsO4) has been determined from collision-induced light-scattering experiments. Our final estimates for these properties are |A|=(84±5)e2a03Eh−1 and |E|=(214±25)e2a04Eh−1. We have also analyzed previous experimental data of the relative permittivity and refractivity of OsO4 to propose the electronic part of the static dipole polarizability of α=51.0e2a02Eh−1. To support our findings we have performed high-level ab initio and density functional theory calculations to obtain theoretical static estimates α=(50.2±1.6)e2a02Eh−1, A=(84±10)e2a03Eh−1, and E=(−252±32)e2a04Eh−1, in essential agreement with the proposed experimental values.
Functional dependence of core-excitation energies
Authors: Takahashi Osamu , Pettersson Lars G. M.
Published: November 2004

We examine in depth the functional dependence of computed core-electron binding and excitation energies based on a total-energy difference approach within Kohn-Sham density functional theory. Twenty-seven functional combinations were studied using a database of reliable experimental data on 18 molecules. The computed core-electron binding energies are largely dependent on the choice of exchange functional. The term value of the first resonant excited state and energy differences between the lowest core-excited states are, however, quite insensitive to the choice of functionals since the errors due to the core-region cancel out. Using these results we define a different exchange functional, which mixes two functionals designed by Perdew and Wang (PD86 and PD91), with the best results for both excitation and binding energies obtained for a mixing ratio 60:40 between these. We also reexamine the relativistic corrections for inner-shell excitations.
Theoretical study of the electronic properties of narrow single-walled carbon nanotubes: Beyond the local density approximation
Authors: Barone Verónica , Scuseria Gustavo E.
Published: November 2004

In this work we present a systematic density functional theory study of the electronic properties of single-walled carbon nanotubes (SWNT) with diameters ranging from 3 to 5 Å. In this work meta-generalized-gradient approximation, hybrid, and screened exchange hybrid functionals are utilized to compute energy band gaps in these narrow SWNT. Our calculations using hybrid functionals show that the only true exceptions to the zone folding predictions are the (4,0) and (5,0) SWNT. The remaining chiral SWNT are semiconducting with band gaps that can be as large as 1.7 eV. However, the calculated energy band gaps are significantly smaller than those predicted by the zone folding scheme. This difference is primarily attributed to the σ-π hybridization present in such narrow SWNT.
Excitation energies of π-conjugated oligomers within time-dependent current-density-functional theory
Authors: van Faassen M. , de Boeij P. L.
Published: November 2004

We study the π*←π singlet excitations of the π-conjugated oligomers of polyacetylene, polydiacetylene, polybutatriene, polythiophene, poly(para-phenylene vinylene), and the lowest singlet excitations of the hydrogen chain. For this we used time-dependent current-density-functional theory within the Vignale–Kohn and adiabatic local density approximations. By studying the dependence of the excitation spectrum on the chain length we conclude that the reduction of the static polarizability when using the Vignale–Kohn functional has two origins. First, the excitation energies of transitions with a large transition dipole are shifted upward. Second, the character of the transition between the lowest occupied and highest unoccupied molecular orbitals and the oscillator strength of the lowest transition within the adiabatic local density approximation is transferred to higher transitions. The lowest transitions that have a considerable oscillator strength obtained with the Vignale–Kohn functional have excitation energies that are in most cases in better agreement with available reference data than the adiabatic local density approximation.
Binomial leap methods for simulating stochastic chemical kinetics
Authors: Tian Tianhai , Burrage Kevin
Published: November 2004

This paper discusses efficient simulation methods for stochastic chemical kinetics. Based on the τ-leap and midpoint τ-leap methods of Gillespie [D. T. Gillespie, J. Chem. Phys. 115, 1716 (2001)], binomial random variables are used in these leap methods rather than Poisson random variables. The motivation for this approach is to improve the efficiency of the Poisson leap methods by using larger stepsizes. Unlike Poisson random variables whose range of sample values is from zero to infinity, binomial random variables have a finite range of sample values. This probabilistic property has been used to restrict possible reaction numbers and to avoid negative molecular numbers in stochastic simulations when larger stepsize is used. In this approach a binomial random variable is defined for a single reaction channel in order to keep the reaction number of this channel below the numbers of molecules that undergo this reaction channel. A sampling technique is also designed for the total reaction number of a reactant species that undergoes two or more reaction channels. Samples for the total reaction number are not greater than the molecular number of this species. In addition, probability properties of the binomial random variables provide stepsize conditions for restricting reaction numbers in a chosen time interval. These stepsize conditions are important properties of robust leap control strategies. Numerical results indicate that the proposed binomial leap methods can be applied to a wide range of chemical reaction systems with very good accuracy and significant improvement on efficiency over existing approaches.
Interpolating moving least-squares methods for fitting potential energy surfaces: Analysis of an application to a six-dimensional system
Authors: Maisuradze Gia G. , Kawano Akio , Thompson Donald L. , Wagner Albert F. , Minkoff Michael
Published: November 2004

The basic formal and numerical aspects of different degree interpolated moving least-squares (IMLS) methods are applied to a six-dimensional potential energy surface (PES) of the HOOH molecule, for which an analytic (“exact”) potential is available in the literature. The results of systematic investigations of the effects of weight function parameters, the degree and partial degree of IMLS, the number of data points allowed, and the optimal automatic point selection of data points up to full third-degree IMLS fits are reported. With partial reduction of cross terms and automatic point selection the full six-dimensional HOOH PES can be fit over a range of 100 kcal/mol to an accuracy of less than 1 kcal/mol with ∼1350 ab initio points.
Atom distributions in binary atom clusters: A perturbational approach and its validation in a case study
Authors: Weigend Florian , Schrodt Claudia , Ahlrichs Reinhart
Published: November 2004

An approach to describe heteroatomic clusters AnBN−n as perturbed homoatomic ones is presented. By first treating the homoatomic systems AN or/and BN and subsequent application of first-order perturbation theory it is possible to estimate relative stabilities of the 2N possible distributions of the atom types A and B at the N atomic sites in a very efficient manner. The approach was tested considering IrnPt13−n as an example (treated with density functional methods). One observes good correlation between relative stabilities estimated from the homoatomic cases and those obtained from explicit treatments of the binary systems. Moreover we rationalize the observed correlation of atom type and atom position in IrnPt13−n.
The static polarizability and first hyperpolarizability of the water trimer anion: Ab initio study
Authors: Chen Wei , Li Zhi-Ru , Wu Di , Gu Feng-Long , Hao Xi-Yun , Wang Bing-Qiang , Li Ru-Jiao , Sun Chia-Chung
Published: November 2004

This work predicts the extraordinary hyperpolarizability of inorganic clusters: two water trimer anions. The first hyperpolarizabilities of (H2O)3− are considerable, β0=1.715×107 a.u. for configuration A and β0=1.129×107 a.u. for configuration B at MP2/d-aug-cc-pVDZ+x level. The first hyperpolarizabilities of (H2O)3− (configuration A) and related systems [(H2O)3 and (H2O)3F−] are compared at the MP2/d-aug-cc-pVDZ+x level. These results are β0=1.715×107 a.u. for (H2O)3−, β0=35 a.u. for (H2O)3 [the neutral core of (H2O)3−], and β0=46 a.u. for (H2O)3F−. Comparing the β0 values of related systems, we find that the dipole-bound excess electron is the key factor in the extraordinary first hyperpolarizability of (H2O)3− species. It will provide a future in the development of some materials with the excess electron (e.g., electrides) that exhibit large nonlinear optical response.
Electron affinities with diffusion quantum Monte Carlo for C2 and BO molecules
Authors: Lu Shih-I
Published: November 2004

To verify the performance of the fixed-node diffusion quantum Monte Carlo method in electron affinities calculations, the adiabatic electron affinities of C2 and BO molecules calculated by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo simulations guiding by trial wave functions constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals are presented in this work. The random walk based results, 3.264(43) and 2.507(32) eV for C2 and BO, respectively, are compared with the available best experimental determined values, 3.269(6) and 2.508(8) eV for C2 and BO, respectively, and the results of other theoretical calculations.
Dissociative recombination study of Na+(D2O) in a storage ring
Authors: Zhaunerchyk Vitali , Ehlerding Anneli , Geppert Wolf D. , Hellberg Fredrik , Thomas Richard D. , Larsson Mats , Viggiano Albert A. , Arnold Susan T. , Österdahl Fabian , Hlavenka Peter
Published: November 2004

The dissociative recombination of Na+(D2O) ion has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The cross section has been measured as a function of center-of-mass energy ranging from 1 meV to 0.1 eV and found to have an E−1.37 dependence. The rate coefficient has been deduced to be (2.3±0.32)×10−7(Te/300)−0.95±0.01 cm3 s−1 for Te=50–1000 K. The branching ratios have been measured at 0 eV. Of the four energetically accessible dissociation channels, three channels are found to occur although the channel that breaks the weak Na+–D2O bond is by far dominant.
Dielectric properties of epitaxial Ba0.6Sr0.4TiO3 films on SiO2∕Si using biaxially oriented ion-beam-assisted-deposited MgO as templates
Authors: Kang B. S. , Lee Jang-Sik , Stan L. , Lee J.-K. , DePaula R. F. , Arendt P. N. , Nastasi M. , Jia Q. X.
Published: November 2004

We have epitaxially deposited Ba0.6Sr0.4TiO3 (BST) thin films on SiO2∕Si substrates using pulsed laser deposition by introducing biaxially oriented ion-beam-assisted-deposited MgO as templates. The structural properties of the BST films were strongly affected by the crystallinity of the templates. The dielectric loss of the BST film was found to decrease as its in-plane texture alignment was improved. As a result, a relatively larger figure of merit K value, defined as tunability∕loss, was obtained for the films with better in-plane crystallinity. The K factor ranged between 7.5 and 3.5 when the in-plane alignment of the MgO templates was varied from 5.0° to 10.5°. This work demonstrates that the crystalline quality of the template layers plays a critical role in monolithic integration of BST with SiO2∕Si for frequency agile devices.
A new localization scheme for the elongation method
Authors: Gu Feng Long , Aoki Yuriko , Korchowiec Jacek , Imamura Akira , Kirtman Bernard
Published: November 2004

A different localization scheme for the elongation method is developed based on regional molecular orbitals. This scheme is more efficient and more accurate than the previous one especially for covalently bonded systems with strongly delocalized π electrons. Ab initio test calculations have been performed on three model systems: water chains, polyglycine, and cationic cyanine chains. The dependence on the size of the starting clusters and the effect of the basis set are investigated. Our results are compared with conventional ab initio calculations and it is found in all cases that the error per added unit levels off to a satisfactorily small value as long as the starting cluster is sufficiently large.
Polarity reversal of the magnetic field induced component of terahertz radiation from InAs surfaces at high density excitation
Authors: Nakajima M. , Oda Y. , Suemoto T. , Saito S.
Published: November 2004

The excitation density dependence of radiation power and wave forms of the terahertz wave from InAs surface under magnetic fields was investigated. A drastic change of the wave forms was observed at high density excitation and was explained by the polarity reversal of the terahertz wave form induced by the magnetic field. The reversal originates from the crossover of the radiation mechanism of the magnetic induced component from the electrons in the accumulation layer to the diffusion current by the photogenerated electrons at high-density excitation under a magnetic field.
Equilibrium bifurcations and chaotic transitions in coupled microlaser lattices
Authors: Riyopoulos S.
Published: November 2004

Analytic and simulation studies for the steady-state equilibria and bifurcations of coupled microlaser arrays are described. Lateral cavity interactions affect the gain in each cavity, leading to active photonic lattice behavior, equivalent to a nonlinear coupled oscillator lattice. The coupled-cavity rate equations are employed to follow the coherent photon and carrier population in each lattice site. Fixed-point-type steady states, of constant lattice phase shift, result for low coupling strengths; the radiation envelope for these states conforms with a periodic Bloch state over the array. Bifurcations to limit cycles of increasing complexity occur at higher coupling via period doubling sequences. The associated spatial patterns of photon and carrier lattice distribution resemble photonic convection cells. Limit cycles of different periods, emanating mathematically from different original fixed points, coexist at high strengths, each one accessible from different initial conditions. The multiplicity of possible limit cycles in systems with many degrees of freedom (number of lattice sites) combined with changes in their accessibility from initial conditions offers new insights to chaotic transitions, compared to low dimensionality paradigms.
Ultrafast electron capture into p-modulation-doped quantum dots
Authors: Gündoğdu K. , Hall K. C. , Boggess Thomas F. , Deppe D. G. , Shchekin O. B.
Published: November 2004

Electron and hole relaxation kinetics are studied in modulation-doped InAs quantum dots using femtosecond time-resolved photoluminescence experiments. We demonstrate that, as a result of doping, carrier relaxation from the barrier layers to the quantum dot ground states is strongly enhanced due to rapid electron–hole scattering involving the built-in carrier population. Results for p-doped quantum dots reveal a threefold decrease in the room-temperature electron relaxation time relative to corresponding undoped quantum dots. Our findings are promising for the development of high-speed, GaAs-based quantum dot lasers with modulation speeds in excess of 30GHz.
Laser operation of a heterojunction bipolar light-emitting transistor
Authors: Walter G. , Holonyak N. , Feng M. , Chan R.
Published: November 2004

Data are presented demonstrating the laser operation (quasicontinuous, ∼200K) of an InGaP–GaAs–InGaAs heterojunction bipolar light-emitting transistor with AlGaAs confining layers and an InGaAs recombination quantum well incorporated in the p-type base region. Besides the usual spectral narrowing and mode development occurring at laser threshold, the transistor current gain β=ΔIc∕ΔIb in common emitter operation decreases sharply at laser threshold (6.5→2.5,β>1).
Fabrication of ambipolar field-effect transistor device with heterostructure of C60 and pentacene
Authors: Kuwahara Eiji , Kubozono Yoshihiro , Hosokawa Tomoko , Nagano Takayuki , Masunari Kosuke , Fujiwara Akihiko
Published: November 2004

Ambipolar field-effect transistor (FET) device was fabricated with heterostructure of thin films of C60 and pentacene. Three types of device structures in the C60∕pentacene heterostructure FET device were studied in order to realize the best ambipolar properties. In the middle-contact type FET device of C60 and pentacene, the mobility μ in p-channel operation was estimated to be 6.8×10−2cm2V−1s−1, while the μ in n-channel operation was 1.3×10−3cm2V−1s−1. This ambipolar FET device is available for a practical building-block to form CMOS integrated circuits with low-power consumption, good-noise margins, and ease of design.
Mn
diffusion in Ga1−xMnxAs∕GaAs superlattices
Authors: Mikkelsen A. , Ouattara L. , Davidsson H. , Lundgren E. , Sadowski J. , Pacherova O.
Published: November 2004

Ga 1 − x Mn x As ∕ GaAs superlattices with Mn concentrations of 1% and 5% in the Ga1−xMnxAs layers and a GaAs spacer thickness of 4 and 60 GaAs monolayers have been studied by cross-sectional scanning tunneling microscopy. By achieving atomic resolution of the superlattices, we observe individual Mn atoms in the Ga1−xMnxAs layers and in the GaAs spacer. We find that about 20% of the total amount of Mn diffuses from the GaMnAs layers into the GaAs spacer layers. Our results can be related to previous measurements of the magnetic properties of short period Ga1−xMnxAs∕GaAs superlattices.
Field-controlled suppression of phonon-induced transitions in coupled quantum dots
Authors: Bertoni Andrea , Rontani Massimo , Goldoni Guido , Troiani Filippo , Molinari Elisa
Published: November 2004

We suggest that order-of-magnitude reduction of the longitudinal-acoustic phonon scattering rate, the dominant decoherence mechanism in quantum dots, can be achieved in coupled structures by the application of an external electric or magnetic field. Modulation of the scattering rate is traced to the relation between the wavelength of the emitted phonon and the length scale of delocalized electron wave functions. Explicit calculations for realistic devices, performed with a Fermi golden rule approach and a fully three-dimensional description of the electronic quantum states, show that the lifetime of specific states can achieve tens of microseconds. Our findings extend the feasibility basis of many proposals for quantum gates based on coupled quantum dots.
Supercontinuum generation in a fiber grating
Authors: Westbrook P. S. , Nicholson J. W. , Feder K. S. , Li Y. , Brown T.
Published: November 2004

We show that supercontinuum generation in a fiber containing a Bragg grating exhibits >10× enhancement near the Bragg resonance wavelength. We also show that the grating dispersion exceeds the waveguide dispersion over a bandwidth far in excess of its photonic band gap. The observed enhancement is consistent with nonlinear Schrödinger equation simulations of the supercontinuum formation that combine grating and waveguide dispersion.
Flexible microprocessor-based evaporation controller
Authors: Meyer zu Heringdorf F.-J. , Belton A. C.
Published: November 2004

Electron beam evaporation sources require two power supplies, one each for the filament current and the electron acceleration. To obtain a stable deposition rate, the emission current between filament and target must remain constant. During film deposition, slight geometry changes in the evaporator cause significant rate variations, making constant readjustment of the emission current necessary. While in commercial solutions, analog feedback regulators are often used to perform this task, these controllers cannot easily be adapted to home-built evaporation sources. The microcontrolled feedback controller presented here is more flexible and versatile than the commercial solutions. The controller can be easily modified to work with different external power supplies and allows the easy upgrade of most existing electron beam evaporation setups. A serial-port computer interface completely integrates the controller into the automated laboratory environment.
AlGaN-based ultraviolet light-emitting diodes grown on AlN epilayers
Authors: Kim K. H. , Fan Z. Y. , Khizar M. , Nakarmi M. L. , Lin J. Y. , Jiang H. X.
Published: November 2004

AlGaN-based deep-ultraviolet light-emitting diode (LED) structures, which radiate light at 305 and 290nm, have been grown on sapphire substrates using an AlN epilayer template. The fabricated devices have a circular geometry to enhance current spreading and light extraction. Circular UV LEDs of different sizes have been characterized. It was found that smaller disk LEDs had higher saturation optical power densities but lower optical powers than the larger devices. This trade-off between power and power density is a result of a compromise between electrical and thermal resistance, as well as the current crowding effect (which is due to the low electrical conductivity of high aluminum composition n- and p-AlGaN layers). Disk UV LEDs should thus have a moderate size to best utilize both total optical power and power density. For 0.85mm×0.85mm interdigitated LEDs, a saturation optical power of 2.9mW (1.8mW) at 305nm (290nm) was also obtained under dc operation.
Terahertz generation by difference-frequency mixing of exciton Wannier–Stark ladder states in biased semiconductor superlattices
Authors: Rosam B. , Leo K. , Yang L. , Dignam M. M.
Published: November 2004

We report the generation of terahertz (THz) radiation in a biased semiconductor superlattice by difference-frequency mixing of interband transitions. The Wannier–Stark spectrum of the superlattice was selectively excited by two spectrally narrow laser lines. The emitted THz radiation was measured as a function of the energetic splitting and spectral position of the bichromatic excitation. The generation of tunable THz radiation is verified. The results clearly show enhanced THz emission when either continuum or 1s exciton wave packets are excited. Good agreement is obtained between the experiment and the results of an exciton model of the nonlinear coherent dynamics.
Growth of highly (100) oriented lead zirconate titanate films on silicon and glass substrates using lanthanum nitrate as a buffer layer
Authors: Choi Jong-Jin , Park Chee-Sung , Park Gun-Tae , Kim Hyoun-Ee
Published: November 2004

Highly oriented lead zirconate titanate [Pb(Zr,Ti)O3; PZT] thin films were deposited on Pt∕Ti∕SiO2∕Si and glass substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was annealed at temperatures between 450 and 550°C, the PZT layer coated onto this buffer layer showed strong (100) orientation. The film deposited on the buffer layer had this orientation, regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature, and heating rate. The lanthanum nitrate buffer layer also acted as a very effective diffusion barrier against Pb–Si interdiffusion, thus allowing for the direct deposition of PZT films on Si, SiO2∕Si, and glass substrates. Using this buffer layer, highly oriented PZT film was fabricated stably and reproducibly, regardless of substrate material and the coating conditions. The nature of the lanthanum nitrate buffer layer and its role in the growth of the highly (100) oriented PZT films were investigated.
Long-range ordered self-assembled InAs quantum dots epitaxially grown on (110) GaAs
Authors: Bauer J. , Schuh D. , Uccelli E. , Schulz R. , Kress A. , Hofbauer F. , Finley J. J. , Abstreiter G.
Published: November 2004

We report on a promising approach for positioning of self-assembled InAs quantum dots on (110) GaAs with nanometer precision. By combining self-assembly of quantum dots with molecular beam epitaxy on previously grown and in situ cleaved substrates (cleaved-edge overgrowth), arrays of long-range ordered InAs quantum dots have been fabricated. Both atomic force microscopy and micro-photoluminescence measurements demonstrate the ability to control size, position, and ordering of the quantum dots. Furthermore, single dot photoluminescence investigations confirm the high optical quality of the quantum dots fabricated.
Overgrowing single crystalline ZnB2O4 on multiwall carbon nanotubes: Straightening the curly tubes
Authors: Yan P. X. , Liu J. Z. , Wang J. , Wu Z. G.
Published: November 2004

Single crystals of ZnB2O4 have been grown from a supercooled molten ZnO-B2O3 system on multiwall carbon nanotubes. Transmission electron microscopy investigations indicated that the originally curly carbon nanotubes were well straightened after the single-crystal coating. The coating and straightening mechanism are discussed.
Spatially resolved measurements of thermal parameters in colloidal suspensions in liquid crystals
Authors: Mercuri F. , Zammit U. , Marinelli M.
Published: November 2004

We report on spatially resolved measurements with a spatial resolution of about 0.1 mm of the transition temperature and of the behavior of the heat capacity, thermal conductivity, and thermal diffusivity over the smectic A–nematic and nematic–isotropic phase transitions in an inhomogeneous aerosil dispersed 8CB liquid crystal. The results were obtained by means of a recently implemented photopyroelectric setup which combines the capability for high temperature resolution measurements with the possibility of visual access in the sample. It is shown that the results relative to different local concentration of particles are consistent with the ones obtained previously on homogeneous samples with different average particle concentration. Finally, the analysis of the local thermal conductivity values has led to an approximate estimate of the local particle concentration in the sample.