bluuebunny/crossref_metadata_2025 huggingface dataset:
Empirical modeling of the peptide amide I band IR intensity in water solution
Authors: Bouř Petr , Keiderling Timothy A.
Published: November 2003

An empirical correction to amide group vacuum force fields is proposed in order to account for the influence of the aqueous environment on the C=O stretching vibration (amide I). The dependence of the vibrational absorption spectral intensities on the geometry is studied with density functional theory methods at the BPW91/6-31G** level for N-methyl acetamide interacting with a variety of of water molecule clusters hydrogen bonded to it. These cluster results are then generalized to form an empirical correction for the force field and dipole intensity of the amide I (C=O stretch) mode. As an example of its extension, the method is applied to a larger (β-turn model) peptide molecule and its IR spectrum is simulated. The method provides realistic bandwidths for the amide I bands if the spectra are generated from the ab initio force field corrected by perturbation from an ensemble of solvent geometries obtained using molecular dynamic simulations.
Interaction of two quasi-monochromatic waves in shallow water
Authors: Onorato M. , Ambrosi D. , Osborne A. R. , Serio M.
Published: November 2003

We study the nonlinear interaction of waves propagating in the same direction in shallow water characterized by a double-peaked power spectrum. The starting point is the prototypical equation for weakly nonlinear unidirectional waves in shallow water, i.e., the Korteweg–de Vries equation. In the framework of envelope equations, using a multiple-scale technique and under the hypothesis of narrow-banded spectra, a system of two coupled nonlinear Schrödinger equations is derived. The validity of the resulting model and the stability of their plane wave solutions is discussed. We show that when retaining higher order dispersive terms in the system, plane wave solutions become modulationally unstable.
Large-scale anisotropy effect on small-scale statistics over rough wall turbulent boundary layers
Authors: Tsuji Yoshiyuki
Published: November 2003

According to the local isotropy hypothesis presented by Kolmogorov, small-scale velocity fluctuations should be universal in any kind of turbulent flow when the Reynolds number is sufficiently large. This is one of the key assumptions in turbulence phenomena. At this stage, the question is not whether this assumption is correct or not, but rather how the local isotropy works as a good approximation depending on the nature of the large-scale anisotropy. In this paper, we report on how the large-scale anisotropy penetrates the small scales. Based on the experiments performed in the strong mean shear flow on the rough-wall boundary layer, we consider how the local isotropy is restored. The anisotropic parameter S* is defined as a ratio of the time scale caused by the mean velocity gradient and the Kolmogorov time scale. It is found that the local isotropy is achieved in the dissipation range even in S*≃0.1. On the other hand, there is no clear evidence of isotropy in the inertial range. Due to the strong mean shear, the second-order structure functions do not satisfy the exact power-law relation but they indicate the convex shape plotted in the logarithmic coordinate. Computing the local slope and the curvature of structure functions, we found they are a strong function of anisotropic parameter.
Reduction of boron thermal diffusion in silicon by high energy fluorine implantation
Authors: El Mubarek H. A. W. , Ashburn P.
Published: November 2003

This letter investigates the effect of a deep F+ implant on the diffusion of boron in silicon. The effects on boron thermal diffusion and transient enhanced diffusion are separately studied by characterizing the diffusion of a buried boron marker layer in wafers with and without a 185 keV, 2.3 ×1015 cm−2 F+ implant, and with and without a 288 keV, 6 ×1013 cm−2 P+ implant. In samples given both P+ and F+ implants, the fluorine completely eliminates the transient, enhanced boron diffusion caused by the P+ implant, and in samples implanted with F+ only, the fluorine suppresses the boron thermal diffusion by 65%. These results are explained by the effect of the fluorine on the vacancy concentration in the vicinity of the boron profile.
A theoretical study on the anomalous pressure dependence of the transport properties of ionic liquids: Comparison among lithium bromide, silica, and water
Authors: Yamaguchi T. , Nagao A. , Matsuoka T. , Koda S.
Published: November 2003

The transport coefficients of three ionic liquids, lithium bromide (LiBr), rubidium bromide (RbBr), and molten silica (SiO2) are calculated by the mixture mode-coupling theory. The static partial structure factors required are obtained from the interionic interaction potential by the Ornstein–Zernike/hypernetted-chain integral equation. The anomalous pressure dependence of the transport properties, the increase in the molar ionic conductivity of LiBr and the fluidity of SiO2 in the low-pressure region, is reproduced qualitatively well by our theoretical calculation. The calculated results are analyzed in the similar way as that for water performed by Yamaguchi et al. [T. Yamaguchi, S.-H. Chong, and F. Hirata, J. Chem. Phys. 119, 1021 (2003)], and we found that the friction on the electric current caused by the coupling between the charge- and number-density modes is effective to the increase of the transport coefficient with pressure, as is the case of water. Comparing the results for LiBr and RbBr, the contribution of the electrostatic friction is smaller for RbBr, which leads to the normal pressure dependence of its molar ionic conductivity. The negative values of the Nernst–Einstein deviation parameter for the ionic conductivity of LiBr and SiO2 reported by previous MD simulations are also explained consistently. Furthermore, it is shown that the mechanism for the anomalous pressure dependence of the fluidity of molten SiO2 demonstrated in this work is consistent with a conventional picture that the five-coordinated silicon atom is important to enhance the ionic mobility.
The infrared absorption spectrum of the gas phase neutral benzoic acid monomer and dimer
Authors: Bakker Joost M. , Mac Aleese Luke , von Helden Gert , Meijer Gerard
Published: November 2003

The IR absorption spectrum of the jet-cooled benzoic acid monomer and dimer have been recorded throughout the 500–1900 cm−1 range via ion dip spectroscopy. Both spectra show a wealth of vibrational modes and the monomer spectrum is remarkably different from that of the dimer. Density functional theory calculations show quantitative agreement with the experimental data. The C–O–H out-of-plane bending vibration in the dimer is poorly reproduced in the theoretical calculations and a more accurate description of the doubly hydrogen bonded structure is therefore still needed.
Quantum chemical modeling of photoabsorption and photoluminescence of the [AlO4] defect in bulk SiO2
Authors: Zyubin A. S. , Mebel A. M. , Lin S. H.
Published: November 2003

Structures, vertical excitation, and photoluminescence energies of the eight lowest electronic states of the [AlO4]0 defect in bulk SiO2 have been calculated using the complete active space self-consistent field, equation-of-motion coupled cluster, outer valence Green functions, and multireference configuration interaction methods within a cluster approximation. Two groups of electronic states with different types of the hole localization on oxygen atoms have been found. In two lower states the unpaired electron is localized on a single O atom, while in the higher energy states this electron is redistributed among two or three O atoms. The excitations to the second group of electronic states are accomplished by photoabsorption in the visible range, whereas photoluminescence energies lie in the infrared region due to significant Stokes shifts.
Mixed quantum-classical study of energy transfer between H2O and a dipeptide
Authors: Wang Mingliang , Zhang J. Z. H.
Published: November 2003

A mixed quantum-classical (MQC) approach is developed to study energy transfer between H2O and Gly-Ala dipeptide. In this approach, the translational motion of H2O is treated classically while the rotational motion of water and the internal torsion of the dipeptide are treated quantum mechanically. This treatment results in a mixed four-dimensional quantum and three-dimensional classical treatment. By employing the AMBER force field, the MQC approach is carried out to study rotational excitation of water and torsional excitation of the dipeptide in collision between H2O and the dipeptide. For excitation of Cα–C and Cα–N torsions, the collisions are direct. In excitation of side chain torsion, the complex collision occurs with the water being trapped near the Gla-Ala. In both direct and resonant collisions, the rotational motion of water is found to be strongly excited. This MQC approach can be extended to study collision energy transfer between rigid small molecules and peptides/protein, polymer or surface. Such theoretical studies should be very useful in understanding detailed energy transfer mechanism involving biological molecules.
Axisymmetric slosh frequencies of a liquid mass in a circular cylinder
Authors: Bian X. , Perlin M. , Schultz W. W. , Agarwal M.
Published: November 2003

Spectral eigenvalue methods along with some lower-dimensional techniques are used to determine the natural frequencies of a liquid slug in a circular tube. The contact lines are either pinned or governed by a slip coefficient assumed small. Corresponding physical experiments are conducted for a borosilicate glass tube and a treated water slug. Gravitational and viscous effects are neglected for the analyses. The spectral results agree well with a simple spherical end cap approximation (zero dimensional) for large aspect ratio slugs and with a membrane approximation (one dimensional) for small aspect ratios. The experimental observations for different aspect ratios agree well with the predictions, although the gravity, viscosity and/or slip are neglected in the analyses.
ac conductance of surface layer in lithium tetraborate single crystals
Authors: Kim Chung-Sik , Park Jong-Ho , Moon Byung Kee , Seo Hyo-Jin , Choi Byung-Chun , Hwang Yoon-Hwae , Kim Hyung Kook , Kim Jung Nam
Published: November 2003

ac conductance for the electrode effect in Li2B4O7 single crystal was investigated by use of a coplanar electrode applied on the surface of a (001) plate. A coplanar electrode in this material more clearly shows conduction of the electrode effect than a conventional parallel planar electrode. The electrode effect in ac conductance is likely to be controlled by the surface layer, which is a poorly conductive depletion layer possibly filled with vacancies of lithium ions. We found that the surface layer is not locally distributed near the electrodes, but, rather, on the broad area of the surface (001) plane of the material. So we conclude that the electrode effect in ac conduction of Li2B4O7 single crystal is mainly due to the poor conductive surface layer distributed over the whole surface of the (001) plane and is not a secondary phase formed by reaction with the electrode material.
Dynamic annealing in ion implanted SiC: Flux versus temperature dependence
Authors: Kuznetsov A. Yu. , Wong-Leung J. , Hallén A. , Jagadish C. , Svensson B. G.
Published: November 2003

A strong influence of ion implantation flux on the accumulation of radiation damage, the so-called dose rate effect, is observed and systematically studied in SiC. 100 keV Si+ ions were implanted into bulk 4H-SiC wafers using different ion fluxes (1.9×1010–4.9×1013 ions/cm2 s) and keeping the implantation dose constant at 5×1014 Si+/cm2. The implants were performed both at room and elevated temperatures, up to 220 °C. Rutherford backscattering spectrometry in the channelling mode using 2 MeV He+ ions was employed to measure ion implantation damage profiles in the samples. For the flux interval used the most, pronounced dynamic annealing effect was detected at 80–160 °C, having an activation energy of 1.3 eV. For example, at 100 °C the amount of disordered Si atoms at the projected ion range is reduced by a factor of 4 by decreasing the ion flux from 4.9×1013 to 1.9×1010 ions/cm2 s. The results are discussed in terms of migration and annihilation of intrinsic type defects for both the Si- and C-sublattices. In addition, two regions for the damage accumulation – at the surface and at the damage peak for 100 keV Si+ ions – are observed.
New developments in the Fourier transform Coulomb method: Efficient and accurate localization of the filtered core functions and implementation of the Coulomb energy forces
Authors: Füsti-Molnár László
Published: November 2003

A new linear scaling approach for the solution of Coulomb problem called the Fourier transform Coulomb (FTC) method has been published recently. Two further developments will be presented in this article. First, an efficient and accurate technique to localize the so-called filtered core functions is introduced, which considerably improves the scaling property of the method and speeds up the most time consuming computational steps by one and two orders of magnitude. An efficient scheme to implement the Coulomb forces is also presented using the localization technique. Besides these methodological developments, detailed results are shown for the scaling property of the computational cost, which is linear in both system and in basis set size. Huge speed ups are achieved compared to the analytical integral evaluation based technique in line with traditional ab initio accuracy requirements. Additionally, ongoing and further possible improvements for every main computational step are also discussed in detail.
Systematically convergent basis sets with relativistic pseudopotentials. I. Correlation consistent basis sets for the post-d group 13–15 elements
Authors: Peterson Kirk A.
Published: November 2003

New correlation consistent-like basis sets have been developed for the post-d group 13–15 elements (Ga–As, In–Sb, Tl–Bi) employing accurate, small-core relativistic pseudopotentials. The resulting basis sets, which are denoted cc-pVnZ-PP, are appropriate for valence electron correlation and range in size from (8s7p7d)/[4s3p2d] for the cc-pVDZ-PP to (16s13p12d3f2g1h)/[7s7p5d3f2g1h] for the cc-pV5Z-PP sets. Benchmark calculations on selected diatomic molecules (As2, Sb2, Bi2, AsN, SbN, BiN, GeO, SnO, PbO, GaCl, InCl, TlCl, GaH, InH, and TlH) are reported using these new basis sets at the coupled cluster level of theory. Much like their all-electron counterparts, the cc-pVnZ-PP basis sets yield systematic convergence of total energies and spectroscopic constants. In several cases all-electron benchmark calculations were also carried out for comparison. The results from the pseudopotential and all-electron calculations were nearly identical when scalar relativity was accurately included in the all-electron work. Diffuse-augmented basis sets, aug-cc-pVnZ-PP, have also been developed and have been used in calculations of the atomic electron affinities.
Systematically convergent basis sets with relativistic pseudopotentials. II. Small-core pseudopotentials and correlation consistent basis sets for the post-d group 16–18 elements
Authors: Peterson Kirk A. , Figgen Detlev , Goll Erich , Stoll Hermann , Dolg Michael
Published: November 2003

A series of correlation consistent basis sets have been developed for the post-d group 16–18 elements in conjunction with small-core relativistic pseudopotentials of the energy-consistent variety. The latter were adjusted to multiconfiguration Dirac–Hartree–Fock data based on the Dirac–Coulomb–Breit Hamiltonian. The outer-core (n−1)spd shells are explicitly treated together with the nsp valence shell with these PPs. The accompanying cc-pVnZ-PP and aug-cc-pVnZ-PP basis sets range in size from DZ to 5Z quality and yield systematic convergence of both Hartree–Fock and correlated total energies. In addition to the calculation of atomic electron affinities and dipole polarizabilities of the rare gas atoms, numerous molecular benchmark calculations (HBr, HI, HAt, Br2, I2, At2, SiSe, SiTe, SiPo, KrH+, XeH+, and RnH+) are also reported at the coupled cluster level of theory. For the purposes of comparison, all-electron calculations using the Douglas–Kroll–Hess Hamiltonian have also been carried out for the halogen-containing molecules using basis sets of 5Z quality.
Orbital optimization: Density matrix-based procedure versus energy minimization
Authors: Guihéry Nathalie , Malrieu Jean-Paul , Evangelisti Stefano
Published: November 2003

An iterative method based on the density matrix block diagonalization has recently been proposed. It includes part of the dynamical correlation in the orbital optimization process and provides either localized or delocalized symmetry adapted molecular orbitals. The present work compares the so-obtained orbitals with the orbitals given by the traditional energy minimization process. Both analytical derivations and numerical calculations on model systems show that the self-consistent field symmetry-breaking problem is avoided when using the density matrix-based procedure in the case of states presenting a left–right resonance, such as mixed valence compounds or bichromophoric molecules. Accurate calculations of excitation energies in a family of magnetic systems, which generally require highly correlated treatments, can also be obtained at a low computational cost when using these appropriate orbitals.
Jones birefringence in gases: Ab initio electron correlated results for atoms and linear molecules
Authors: Rizzo Antonio , Coriani Sonia
Published: November 2003

The results of an ab initio investigation of the Jones birefringence (JB) of noble gases (He, Ne, Ar, Kr) and of a few linear molecules—both centrosymmetric (H2,N2,C2H2) and dipolar (CO)—carried out employing coupled cluster response techniques and rather extended correlation-consistent basis sets are presented. The relationships existing between the appropriate linear, quadratic, and cubic frequency-dependent response functions and the tensors introduced in the theoretical derivation of the anisotropy by Graham and Raab in 1983 [Proc. R. Soc. London, Ser. A, 390, 73 (1983)] are introduced. The magnitude of the effect is determined and comparison is made with that of the Cotton–Mouton effect (CME), which, together with the Kerr effect, is closely related to Jones birefringence and superimposed to it in actual measurements, and of electric field gradient induced birefringence (EFGB). CME yields anisotropies of the refractive index ≈100 to ≈3500 larger than those predicted for JB in the eight systems studied, whereas EFGB and JB are shown to be of comparable strength.
A theoretical investigation on the mechanism and kinetics for the reaction of atomic O(3P) with CH3CHCl2
Authors: Zhang Qingzhu , Wang Shaokun , Gu Yueshu
Published: November 2003

The reaction of atomic O(3P) with CH3CHCl2 has been studied theoretically using ab initio direct dynamics methods for the first time. This reaction involves two channels: H abstraction from the methyl group (CH3), and H abstraction from the methyne group (CH). Two nearly degenerate saddle points of A″3 and A'3 symmetries have been located for each hydrogen abstraction channel. At the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) level, the potential barrier of H abstraction from the CH3 group is higher about 6 kcal/mol than that of H abstraction from the CH group. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction paths for all the channels are discussed and compared. On the basis of the ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory with small-curvature tunneling correction method over a wide temperatures range of 200–3000 K. The theoretical results have been compared with available experimental data. The kinetics calculations show that the variational effect is small and in the low temperature range (200–800 K), the small curvature tunneling contribution is important for all the channels. The detailed branching ratios have been discussed.
An intrinsic reaction coordinate calculation of the torsional potential in ethane: Comparison of the computationally and experimentally derived torsional transitions and the rotational barrier
Authors: Halpern Arthur M. , Glendening Eric D.
Published: November 2003

Intrinsic reaction coordinate (IRC) calculations of the torsional potentials of C2H6, CH3CD3, and C2D6 have been carried out at the MP2/6-31++G** level. The C2H6 potential was corrected at the coupled-cluster single double (triple) [CCSD(T)] level with extrapolation to the complete basis set limit (CBS). For CH3CD3 and C2D6, the MP2 potentials were scaled by 0.862 to approximate CCSD(T)/CBS results. The IRC potential for the D3h→D3d relaxation in C2H6 was fit to a two-term Fourier series containing V3 and V6 coefficients for which the barrier height, V3, was set to the CCSD(T)/CBS value (941 cm−1), and V6 was optimized at 6.7 cm−1. Sixfold torsional potentials were constructed from the CCSD(T)/CBS profiles and the resulting eigenvalues were used to calculate the Δn(ν4)=2 transitions, which are compared with experimental assignments. Comparisons are also made with observed IR transitions. Our best estimate of the rotational barrier is 941 cm−1. This value, as well as other high-level ab initio results, is about 50 cm−1 smaller than the V3 parameter obtained from the analysis of microwave and Raman data. The one-dimensional IRC potential neglects subtle coupling of ethane’s torsional motion to other modes and is likely responsible for the small, but systematic, differences between the calculated and experimental results.
Unusual pickup statistics of high-spin alkali agglomerates on helium nanodroplets
Authors: Vongehr Sascha , Kresin Vitaly V.
Published: November 2003

The pickup of alkali atoms by helium nanodroplets is unusual in that these atoms are not wetted and enveloped by the liquid, but reside in weakly binding surface dimples. As a result, it has been suggested that the alkali clusters which assemble on droplet surfaces must exist in spin-polarized states with a low condensation energy. We consider the size distribution statistics which would be exhibited by the alkali agglomerates in such a case, and show that it would be very different from the conventional Poisson shape. A careful measurement of the variation of the intensities of droplet-grown alkali clusters with size and/or vapor pressure in the pickup region may be able to test the giant-spin hypothesis.
Optimization of the semiclassical initial value representation of the exact quantum-mechanical real time propagator
Authors: Zhang Shesheng , Pollak Eli
Published: November 2003

The recently derived exact representation of the quantum propagator in terms of semiclassical initial value representations (SCIVR) is used to optimize the width parameter in the SCIVR. Minimization of the expectation value of the correction operator related to the SCIVR leads to improved convergence of the representation. A test on a model one-dimensional double-well potential demonstrates that this optimization can give essentially exact results using only the first two terms in the SCIVR expansion of the exact propagator.
On the Brinkman correction in unidirectional Hele-Shaw flows
Authors: Zeng Jie , Yortsos Yannis C. , Salin Dominique
Published: November 2003

We study the Brinkman correction to Darcy’s equation for unidirectional flows in a Hele-Shaw cell. Three examples, describing gravity-driven flow with variable density, pressure-driven flow with variable viscosity, and pressure-driven flow in a cell with a specific variation in aperture are discussed. In general, the Brinkman correction involves nonlocal terms, and it is not simply equal to an effective viscous shear stress involving the gap-averaged velocity. The latter is applicable at long wavelengths, however, provided that the viscosity is augmented by a prefactor equal to 12/π2.
Topographic effects on establishment of selective withdrawal
Authors: Jamali Mirmosadegh
Published: November 2003

This study is concerned with evolution of selective withdrawal of a linearly stratified fluid through a line sink at the base of a reservoir with bottom topography in the form of a sill of small height. The problem is investigated theoretically in the linear, inviscid limit using a perturbation technique. The induced flow due to motion of the first few shear waves is studied. It is shown that the effect of a sill on the flow field is confined mostly to the withdrawal layer in the vicinity of the sill. Equations are proposed for the steady withdrawal layer thickness and the critical Froude number in the presence of a sill.
Visualization of magnetoconvection
Authors: Andreev O. , Thess A. , Haberstroh Ch.
Published: November 2003

The opacity of liquid metals represents a seemingly insurmountable barrier for visualizing flows of electrically conducting fluids under the influence of a magnetic field. We demonstrate that this fundamental limitation of experimental magnetohydrodynamics (MHD) can be overcome by using (transparent) electrolytes in place of (opaque) liquid metals if a superconducting magnet with field strength of the order of 10 Tesla is used instead of traditional electromagnets. We study the Rayleigh–Bénard convection as a prototype problem under a horizontal magnetic field using a shadowgraph method and tracer particles. It is shown that recent observations of Burr and Müller [J. Fluid Mech. 453, 345 (2002)] of an increased heat transfer in magnetoconvection can be attributed to the two-dimensionality and a smaller length scale of motion due to the magnetic field. The present approach provides a rational framework for the application of modern optical flow measurement techniques like laser Doppler velocimetry and particle image velocimetry to MHD problems.
Study of the low temperature ordering of L1–Fe–Pt in Fe/Pt multilayers
Authors: Endo Yasushi , Oikawa Katsunari , Miyazaki Takamichi , Kitakami Osamu , Shimada Yutaka
Published: November 2003

In order to clarify the formation process of L10 Fe–Pt ordered phase in Fe (tFe)/Pt (tPt) multilayers, we have evaluated the activation energy of ordering (QS) and of atomic interdiffusion at Fe/Pt interfaces (QD). QS for the multilayers takes a minimum value of ∼0.7 eV when tFe=tPt, much lower than that of Fe–Pt disordered alloy films (1.2 eV). This value is almost the same with the activation energy QD of atomic interdiffusion at Fe/Pt interfaces. From these results, it is concluded that the interdiffusion at Fe/Pt interfaces which occurs at relatively low temperature dominates the formation process of L10 Fe–Pt in Fe/Pt multilayers.
Dressed molecule theory for liquids and solutions: An exact charge renormalization formalism for molecules with arbitrary charge distributions
Authors: Ramirez Rosa , Kjellander Roland
Published: November 2003

An exact statistical mechanical theory for fluid mixtures of rigid molecules with arbitrary charge distributions, sizes, and shapes is presented. It deals with many-body effects in electrostatic interactions between molecules in fluids and can, for example, be applied to mixtures of polar molecules and to solutions of electrolytes or colloidal dispersions in polar molecular solvents. All solute and solvent molecules are treated on the same fundamental level in statistical mechanics. The exact screened Coulomb potential φ0(r) for the solution is given a general definition. A renormalized charge distribution ρi0 for each molecule of any species i is uniquely defined such that the total electrostatic potential from each i molecule is exactly given by φ0 with ρi0 as the source. By using ρi0 when calculating the interaction between the molecule and the total electrostatic potential from any source, one includes the indirect effects from the surrounding polarizable molecular medium on the electrostatic part of the potential of mean force for the molecule. In general, all kinds of molecules (charged, polar, and apolar ones) acquire renormalized charges in electrolyte solutions. The dielectric function and other fundamental properties of the mixture can be expressed in terms of ρi0 for all species. The formally exact theory is expressed in a Poisson–Boltzmann (PB)-type manner by using the renormalized rather than actual (bare) charges and it is shown that the total electrostatic potential due to a molecule satisfies an equation that is the exact version of the linear PB equation. The decay behaviors of φ0, the pair potential of mean force and pair distribution functions are investigated.
Microscopic calculation of the energetics of ions in polyethylene
Authors: Eilmes A. , Munn R. W. , Góra A.
Published: November 2003

Polarization energies are calculated for a point charge ion in amorphous polyethylene using local segment and non-local distributed molecular polarizabilities with material structures simulated by both general-purpose and specialist Monte Carlo software. An expression is derived for the polarization energy of a molecular system divided into submolecules that may acquire both induced dipoles and induced charges in the presence of external charges. The two descriptions of the molecular response lead to results that generally differ only because of the polarizability difference, so that less computationally demanding local polarizabilities may suffice, with results for distributed response estimated by suitable scaling. The polarization energy is correlated with the molecular packing around the ion and its position in the polymer material through fluctuations of the polymer density. The polarization energy distribution from the general-purpose software has a range of some ±0.6 eV about a maximum at −1 eV and from the specialist software has a range of some ±0.5 eV centered about a maximum at −1.5 eV, both for a density of 0.8 g cm−3. Relaxation of the sample after inserting the ion lowers the polarization energy by typically 0.5 eV and broadens the distribution. The results for polyethylene as a test system suggest that the methodology may be applied to more complicated systems, such as practical polymer electrolytes.
Turbulent-viscosity reduction mechanism based on anisotropic turbulence effects
Authors: Yoshizawa Akira
Published: November 2003

The relationship between turbulent viscosity and turbulence anisotropy is investigated on the basis of a statistical theory of inhomogeneous turbulence. An anisotropic turbulent viscosity is derived with the axisymmetric anisotropy subject to an enhanced streamwise turbulence intensity taken into account. The result paves the way for explaining a mechanism of drag reduction due to the change of turbulence anisotropy in a developed pipe flow. The drag reduction by polymer additives is discussed in light of this mechanism.
Group-theoretical analysis of the electronic structure data for molecular ions C60N± (Ih) derived from multipole expansion of the Coulomb interelectronic interactions
Authors: Plakhutin Boris N.
Published: November 2003

The paper presents a group-theoretical analysis of the new approach to calculating molecular ions C60N± (Ih) based on the multipole expansion of interelectronic interactions and of the results of calculations presented by Nikolaev and Michel (NM) [J. Chem. Phys. 117, 4761 (2002)]. By combining the NM method with the theory of “integral invariants” developed by Plakhutin and Judd & Lo, we represent the basic formulas and quantities of the former method in the symmetry-reduced form corresponding to a full separation of variables. This enables us to derive two general relationships between multipole expansion data for complementary configurations, electronic γN and hole (γ+)N. These relationships are used to correct the numerical data (coefficients of the multipole expansion and the energies of the states) presented by NM for the hole configurations (t1u+)N and (hu+)N. Some new possible applications of the modified (symmetry-reduced) NM method are discussed.
Electrically detected magnetic resonance of ion-implantation damage centers in silicon large-scale integrated circuits
Authors: Umeda T. , Mochizuki Y. , Okonogi K. , Hamada K.
Published: November 2003

We used electrically detected magnetic resonance to study the microscopic structure of ion-implantation-induced point defects that remained in large-scale Si integrated circuits (Si LSIs). Two types of defects were detected in the source/drain (n+-type) region of 0.25-μm-gate-length n-channel metal oxide semiconductor field-effect-transistors on LSIs: (i) a spin-1 Si dangling-bond (DB) pair in divacancy–oxygen complexes (DB–DB distance, R≈0.6 nm); and (ii) a series of larger Si vacancies involving distant Si DBs (R⩾1.4 nm). These vacancy-type defects were much more thermally stable in Si LSIs than those in bulk Si crystals. We suggested two physical mechanisms for this enhanced stability: internal mechanical stress and oxygen incorporation in the active regions of LSIs. After examining the relationship between the defects and current–voltage characteristics, we concluded that these defects are distributed in the near-surface n+-type region close to the gate and that they are the source of the gate-induced drain leakage currents.
Quenching of cathodoluminescence from Eu3+-doped La2O2S
Authors: Bang Jungsik , Abrams Billie , Holloway Paul H.
Published: November 2003

Quenching of the cathodoluminescent (CL) efficiency of La2O2S:Eu3+ prepared by combustion reaction was investigated by measuring the temporal dependence of the CL intensities. While the emission intensity corresponding to the D05⇒F27 electronic transition of Eu3+ did not change at a low current density (e.g., 65 μA/cm2), it decayed over the first 5 s of irradiation at a high current density (e.g., 500 μA/cm2). In addition, the difference between the initial and steady-state emission intensities increased as the current density increased. Based on thermal quenching data for the D05⇒F27 transition, the quenching observed at high current densities was only partially explained by electron-beam heating. In addition to changes in intensity, the ratio of the CL intensities from the D15 transition (D05⇒F27) and the D05 transition (5D0⇒7F2) (designated D15/D05) also decreased with increasing current density during the first ∼5 s of electron irradiation. Based upon measurement of the Auger electron peak energies, it is suggested that surface voltage changes due to charging cannot explain these changes. Instead, it is postulated that local redistribution of charge carriers over the range of the primary electron beam result from induced internal electron field. The effects of these internal electric fields on the magnitude and classification of interactions of the excited Dj5 state of Eu3+ are discussed.
Quantum confinement energy in nanocrystalline silicon dots from high-frequency conductance measurement
Authors: Huang Shaoyun , Banerjee Souri , Tung Raymond T. , Oda Shunri
Published: November 2003

Electron charging and discharging processes in floating gate metal–oxide–semiconductor memory based on nanocrystalline silicon (nc-Si) dots were investigated at room temperature using capacitance–voltage and conductance–voltage (G–V) measurements. From charged nc-Si dots, a sequential electron discharging processes was clearly observed in G–V spectroscopy. The fine structure in the observed conductance peaks has been interpreted in terms of the Coulomb blockade and quantum confinement effects of nc-Si dots, which allowed the electron-addition energy to be estimated at 50 meV. Taking the electron-charging energy between the silicon substrate and the floating dot (30 meV) into account, the quantum confinement energy was found to be as significant as the electron charging energy for nc-Si dots, with ∼8 nm in diameter, embedded in silicon oxide.
Thermopower peak in phase transition region of (1−x)La2/3Ca1/3MnO3/(x)yttria-stabilized zirconia
Authors: Liu Wei , Zhao Jun , Chen Chinping , Yan Shousheng , Xia Zhengcai , Liu Sheng
Published: November 2003

The thermoelectric power (TEP) and the electrical resistivity of the intergranular magnetoresistance composite (1−x)La2/3Ca1/3MnO3/(x)yttria-stabilized zirconia (YSZ) (LCMO/YSZ) with x=0%, 0.75%, 1.25%, 4.5%, 13%, 15%, and 80% of YSZ have been measured from 300 down to 77 K. A pronounced TEP peak appears during phase transition for samples with x>0, while it is not observed for x=0. We suggest that this is due to the magnetic structure variation induced by lattice strain which is a result of the LCMO/YSZ boundary layers. The transition width in the temperature derived from dχ/dT, with χ the ac magnetic susceptibility, supports this interpretation.
Synchrotron radiographic study and computer simulation of reactions between micropipes in silicon carbide
Authors: Gutkin M. Yu. , Sheinerman A. G. , Argunova T. S. , Mokhov E. N. , Je J. H. , Hwu Y. , Tsai W.-L. , Margaritondo G.
Published: November 2003

By using synchrotron radiation phase sensitive radiography we have examined the reactions of screw superdislocations or micropipes in silicon carbide single crystals: bundling, twisting, and splitting. To understand the nature of these reactions, a model of micropipe motion during crystal growth has been proposed. Based on this model, a computer simulation of the evolution of a random micropipe ensemble has been performed. The simulation demonstrates that the coalescence of micropipes with opposite-sign Burgers vectors may be realized in two ways: (i) their straightforward movement towards each other or (ii) their revolution about one another. Twisted dislocation dipoles arise when two micropipes are under strong influence of the stress fields from dense groups of other micropipes. The transformation of dipoles into semiloops as well as the annihilation of micropipes result in diminishing of their average density.
Experimental study and modeling of reverse-bias dark currents in PIN structures using amorphous and polymorphous silicon
Authors: Tchakarov S. , Roca i Cabarrocas P. , Dutta U. , Chatterjee P. , Equer B.
Published: November 2003

Polymorphous silicon (pm-Si:H) is a nanostructured silicon thin film, with a lower defect density of states and better electronic properties than standard amorphous silicon. We have studied the reverse-bias dark current in PIN structures using this material as the intrinsic layer and compared the results to amorphous silicon PIN devices. All the structures were grown using a standard plasma enhanced chemical vapor deposition process. For thick pm-Si:H devices, we have achieved reverse-bias dark current densities about ten times lower than those obtained using amorphous silicon as the intrinsic layer. This is consistent with the lower defect density of states in polymorphous silicon, which is about 7×1014 cm−3 against 5×1015 cm−3 for amorphous silicon. For a 2.5-μm-thick pm-Si:H diode, the current density obtained is as low as 3 pA cm−2 at −3 V. However, for thinner structures (∼0.5 μm), polymorphous and amorphous silicon show nearly the same reverse-bias leakage current. The experimental dark as well as illuminated characteristics of the diodes have been simulated using a model that incorporates field enhanced thermal generation under reverse-bias conditions (Poole–Frenkel effect). Results reveal that in pm-Si:H diodes, the P/I interface is much more defective than in standard a-Si:H PIN diodes. This fact is shown to completely mask the advantage of the lower defect density of pm-Si:H, in thin PIN diodes. However, in thick samples the electric field in the device and, therefore, also the Poole–Frenkel enhancement of thermal generation are smaller. The effect of the lower density of states in polymorphous silicon is then dominant, and we have achieved a dark current density of 3 pA cm−2 at −3 V for a 2.5-μm-thick diode, as already stated.
Carbon-13 nuclear magnetic resonance study on poly(ethylacrylate-co-sodium acrylate) ionomer
Authors: Lim Ae Ran , Kwark Young-Je , Kim Joon-Seop
Published: November 2003

The poly(ethylacrylate) (PEA) homopolymer and poly(ethylacrylate-co-sodium acrylate) ionomer that contain 8.4 mol % ionic groups (PEANa-8.4) were studied by C13 using cross polarization and magic angle spinning nuclear magnetic resonance (CP/MAS NMR). The C13 spin-lattice relaxation times in a rotating frame, T1ρ, were measured as functions of the temperature. Using these T1ρ spin-lattice relaxation times, we addressed the chain mobility, correlation time, and activation energy for carbon of the PEA homopolymer and the PEANa-8.4 ionomer. We found that the molecular motion in the PEA homopolymer needed a higher activation energy than that in the PEANa-8.4 ionomer. In addition, we observed that motion of the 1-methyl carbons in the PEANa-8.4 ionomer was distinctly different from that in the PEA homopolymer: the value of T1ρ for 1-methyl carbon is ascribed to stronger interactions between the polymer chains in the homopolymer.
Particle image velocimetry study on the pattern formation in a vertically vibrated granular bed
Authors: Deng Rensheng , Wang Chi-Hwa
Published: November 2003

In this paper, a two-dimensional particle image velocimetry (PIV) system was used to examine the f/2 stripe pattern forming in a vertically vibrated granular layer. Since the PIV sampling frequency does not match with the vibrating frequency, a special identification-coupling method was adopted to combine the images taken in different cycles to offer the information in one complete cycle. The measured velocity vectors showed exactly the particle motions at various stages of a motion cycle, illustrating the alternating peaks and valleys on the layer top. Furthermore, quantitative results on the temporal evolution of velocity profiles were obtained and some other interesting phenomena were observed, such as the appearance of local structures (e.g., dual-phase layer structure) and the moving feature of the “standing point.” The mechanism accounting for the occurrence of stripes on the surface is discussed.
Relative equilibria of singly periodic point vortex arrays
Authors: Stremler Mark A.
Published: November 2003

This paper presents a systematic investigation of singly periodic discrete vortex configurations that move uniformly without change of shape or size. The general condition for existence of such equilibria is that SV̄=0, where S=∑Γ is the net circulation within a single period and V̄ is (the complex conjugate of) the vortex velocity. Those configurations that satisfy this condition are determined for two and three vortices per period.
Effective eddy viscosities in implicit large eddy simulations of turbulent flows
Authors: Domaradzki J. Andrzej , Xiao Z. , Smolarkiewicz Piotr K.
Published: November 2003

We propose a method for computing effective numerical eddy viscosity acting in dissipative numerical schemes used in monotonically integrated large eddy simulations of turbulence. The method is evaluated on an example of a specific nonoscillatory finite volume scheme MPDATA developed for simulations of geophysical flows.
Hydrodynamic dispersion in confined packed beds
Authors: Maier Robert S. , Kroll Daniel M. , Bernard Robert S. , Howington Stacy E. , Peters John F. , Davis H. Ted
Published: November 2003

Pore-scale simulations of monodisperse sphere packing and fluid flow in cylinders have reproduced heterogeneities in packing density and velocity previously observed in experiment. Simulations of tracer dispersion demonstrate that these heterogeneities enhance hydrodynamic dispersion, and that the degree of enhancement is related to the cylinder radius, R. The time scale for asymptotic dispersion in a packed cylinder is proportional to R2/D̂T, where D̂T represents an average rate of spreading transverse to the direction of flow. A generalization of the Taylor–Aris model of dispersion in a tube provides qualitative predictions of the long-time dispersion behavior in packed cylinders.
Effectiveness of a drag reducing polymer: Relation to molecular weight distribution and structuring
Authors: Vlachogiannis M. , Liberatore M. W. , McHugh A. J. , Hanratty T. J.
Published: November 2003

Solutions of partially hydrolyzed polyacrylamide were degraded by intermittent circulation through a large pump in a turbulent flow loop. Measurements of pressure drop, fluid turbulence, molecular weight distribution, and viscosity were made. Rheo-optical studies were also carried out to explore the propensity of solutions to form structures under simple shear flow. Degradation was not accompanied by significant changes in the molecular weight distributions. This observation suggests that, for the system studied, clusters or aggregates of polymers have a more important effect on the turbulence than individual molecules. Therefore, degradation occurs by the destruction of these clusters. This result is consistent with the observation that larger drag reductions are realized by the injection of concentrated polymer solutions into a water flow.
Electronic structure of La0.7Sr0.3MnO3 thin films for hybrid organic/inorganic spintronics applications
Authors: de Jong M. P. , Dediu V. A. , Taliani C. , Salaneck W. R.
Published: November 2003

Recently, hybrid organic/inorganic interfaces have been used in prototype spin valves, with thin films of La0.7Sr0.3MnO3 as the spin-polarized charge carrier injecting electrode. We have used x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy to study the surface properties of La0.7Sr0.3MnO3 thin films prepared by the channel-spark ablation technique. In particular, preparation of the surfaces by annealing in ultra-high-vacuum surface segregation, the valence electronic structure and work function were studied in order to provide important information for charge injection behavior. It is shown that annealing in vacuum at T<500 °C removes surface contamination and stabilizes oxygen content. The work-function values change from 4.2 to 4.8 eV depending on surface treatment. A surface layer consisting of SrO and SrCO3 of a few angstrom thick was found, which can significantly influence the spin injection properties at the interfacial region.
Photoresponse of Zener tunneling junctions of Pb(Ti,Zr)O3/SrTiO3 at low temperature
Authors: Watanabe Yukio , Okano Motochika
Published: November 2003

Temperature (T) dependent current–voltage (IV) characteristics of epitaxial Pb(Ti,Zr)O3/SrTiO3 heterojunctions exhibiting the characteristics of Zener tunneling are measured in the dark and in the light. Ultraviolet light is found to induce a prominent photovoltaic effect at all T down to at least 50 K, while the open circuit voltage increases with decreasing T. In the dark the reverse bias current increases with decreasing T. In the light the reverse bias current at low T is a superposition of a photovoltaic current and a small component that is identical to the reverse bias current in the dark. These observations indicate that the anomalous T dependence of the reverse bias current in the dark is attributable to the tunneling from the Pb(Ti,Zr)O3 band to the SrTiO3 band. Additionally, short pulse voltages modulate the tunneling current, which is retained.
Midinfrared electroluminescence in quantum cascade structures with InP/InGaAs active regions
Authors: Troccoli Mariano , Capasso Federico , Chen Jianxin , Peabody Milton L. , Gmachl Claire , Sivco Deborah L. , Chen Cheng-Hsuan , Cho Alfred Y.
Published: November 2003

We report on the midinfrared emission from electroluminescent devices with quantum cascade active regions based on InGaAs/InP heterostructures. We observe emission at λ∼12 μm from two different structures and compare their emission characteristics based on the different band structure designs. Their relevance in view of the realization of InP-based quantum cascade lasers with aluminum-free waveguides is discussed.