bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic pinning in superconductor-ferromagnet multilayers
Authors: Bulaevskii L. N. , Chudnovsky E. M. , Maley M. P.
Published: July 2002

We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 106−107 A/cm2 at high temperatures (but not very close to Tc) at least in magnetic fields below 0.1 T.
Germanium/carbon core–sheath nanostructures
Authors: Wu Yiying , Yang Peidong
Published: July 2002

Germanium/carbon core–sheath nanostructures and junctions are produced when Ge nanowires are subject to a thermal treatment in an organic vapor doped vacuum. The organic molecules pyrolyze on the surface of the Ge nanowires and form a continuous graphitic coating. The carbon-sheathed Ge nanowires undergo melting and evaporation at high temperature, which results in the formation of germanium/carbon junctions. These core–sheath nanostructures and junctions generally have diameters of 5–100 nm, sheath thickness of 1–5 nm, and lengths up to several micrometers. This process may prove to be an effective approach to prevent the nanowire surface oxidation and create nanowires with chemically inert surface.
Covariant field theory on frame bundles of fibered manifolds
Authors: McLean M. , Norris L. K.
Published: July 2002

We show that covariant field theory for sections of π : E→M lifts in a natural way to the bundle of vertically adapted linear frames LπE. Our analysis is based on the fact that LπE is a principal fiber bundle over the bundle of 1-jets J1π. On LπE the canonical soldering 1-forms play the role of the contact structure of J1π. A lifted Lagrangian ℒ: LπE→R is used to construct modified soldering 1-forms, which we refer to as the Cartan–Hamilton–Poincaré 1-forms. These 1-forms on LπE pass to the quotient to define the standard Cartan–Hamilton–Poincaré m-form on J1π. We derive generalized Hamilton–Jacobi and Hamilton equations on LπE, and show that the Hamilton–Jacobi and canonical equations of Carathéodory–Rund and de Donder–Weyl are obtained as special cases.
Drift-like dust-convective cells in a dusty magnetoplasma
Authors: Mamun A. A. , Shukla P. K.
Published: July 2002

A theoretical investigation has been made of an obliquely propagating low-frequency electrostatic dust-convective cell mode in a nonuniform dusty magnetoplasma, taking account of both the unbounded and bounded plasma situations. It has been shown that for (kd/k)2≫ωcd/ωci, where kd is the inverse of the dust density inhomogeneity scalelength, k is the wave number, and ωcd (ωci) is the gyrofrequency of the dust particle (ion), there exists a new drift-like dust-convective cell mode characterized by the frequency ω≃ωcdk/kd (when the density gradient is positive) or ω≃ωci|kd|/k (when the density gradient is negative). The dispersion properties of the obliquely propagating dust-convective cell mode as well as our newly found mode are found to be significantly modified by the effects of finite cylindrical/slab boundaries. The implications of our results in both space and laboratory dusty plasma environments are briefly discussed.
Near edge x-ray absorption fine structure of thermally annealed amorphous nitrogenated carbon films
Authors: Bhattacharyya Somnath , Lübbe M. , Richter F.
Published: July 2002

The change of structure of tetrahedral amorphous carbon (ta-C) films after nitrogen incorporation, particularly at a high concentration, was studied by near edge x-ray absorption fine structure (NEXAFS) spectroscopy and it was found to be very close to pyridine. The π* peak at the N K (nitrogen K) edge was decomposed into three components corresponding to different resonances. From a detailed analysis of N K edge by NEXAFS spectroscopy it was revealed that as the nitrogen concentration in the films increases, the σ*/π* intensity ratio decreases, indicating that there is an increase of the amount of C=N relative to the C–N bonds. By thermal annealing at different temperatures, up to 800 °C, the nitrogen concentration in the films is reduced. Intensity as well as the position of the π* peak at the C K edge changed with annealing temperature. At the same time, a decrease of the intensity of the π* peak at the N K edge and a very interesting change of the relative intensities of the three split components of this π* peak have been observed. The possible changes of structure of nitrogenated carbon films by annealing and thermal stability of the films have been thoroughly emphasized.
Orientation of chiral heptahelicene C30H18 on copper surfaces: An x-ray photoelectron diffraction study
Authors: Fasel R. , Cossy A. , Ernst K.-H. , Baumberger F. , Greber T. , Osterwalder J.
Published: July 2002

The orientation and the intramolecular relaxation due to adsorption of the chiral phenanthrene-derivative heptahelicene, C30H18, on Cu(111) and Cu(332) surfaces have been investigated by means of angle-scanned full-hemispherical x-ray photoelectron diffraction. Although the C 1s diffraction patterns of the adsorbed submonolayer coverage helicene films exhibit scattering anisotropies of less than two percent, a detailed analysis involving simple molecular mechanics calculations of the atomic coordinates, photoelectron diffraction single-scattering cluster calculations and an R-factor analysis permits the determination of the helicene molecular orientation. On Cu(111), the molecules are found to bind to the substrate surface via their terminal phenanthrene group oriented parallel to the surface plane, while on Cu(332) the three terminal C-6 rings are oriented parallel to the (111) terrace plane. Six azimuthal molecular orientations are found to coexist on Cu(111), on Cu(332), however, the step–molecule interaction leads to a unique azimuthal alignment of the heptahelicene molecules. The heptahelicene on Cu(332) system thus represents a chiral surface with single-phase orientational order.
The effect of an external magnetic field on oscillatory instability of convective flows in a rectangular cavity
Authors: Gelfgat A. Yu. , Bar-Yoseph P. Z.
Published: July 2002

The present study is devoted to the problem of onset of oscillatory instability in convective flow of an electrically conducting fluid under an externally imposed time-independent uniform magnetic field. Convection of a low-Prandtl-number fluid in a laterally heated two-dimensional horizontal cavity is considered. Fixed values of the aspect ratio (length/height=4) and Prandtl number (Pr=0.015), which are associated with the horizontal Bridgman crystal growth process and are commonly used for benchmarking purposes, are considered. The effect of a uniform magnetic field with different magnitudes and orientations on the stability of the two distinct branches (with a single-cell or a two-cell pattern) of the steady state flows is investigated. Stability diagrams showing the dependence of the critical Grashof number on the Hartmann number are presented. It is shown that a vertical magnetic field provides the strongest stabilization effect, and also that multiplicity of steady states is suppressed by the electromagnetic effect, so that at a certain field level only the single-cell flows remain stable. An analysis of the most dangerous flow perturbations shows that starting with a certain value of the Hartmann number, single-cell flows are destabilized inside thin Hartmann boundary layers. This can lead to destabilization of the flow with an increase of the field magnitude, as is seen from the stability diagrams obtained. Contrary to the expected monotonicity of the stabilization process with an increase of the field strength, the marginal stability curves show nonmonotonic behavior and may contain hysteresis loops.
Rotational spectroscopy of IO X 2Πi
Authors: Miller Charles E. , Cohen Edward A.
Published: July 2002

Pure rotational spectra of the IO radical have been observed for vibrational levels up to v=13 in the X1 Π3/22 state and up to v=9 in the X2 Π1/22 state. Isotopically enriched I18O rotational spectra have been observed for vibrational levels up to v=5 in both the X1 and X2 states. These are the first high-resolution spectra of any kind reported for the X2 state and greatly extend the available data for the X1 state. The data for both isotopomers have been fitted simultaneously to a single set of Π2 parameters with fixed isotopic ratios. The isotope relations among the parameters have provided a means of decorrelating the electron spin-rotation constant γ from the fine-structure centrifugal distortion constant, AD, and have allowed the first determination of an effective value for γ. The rotation–vibration constants correspond to the equilibrium molecular properties re(X1)=186.762 pm, re(X2)=188.468 pm, ωe(X1)=681.69 cm−1, and ωe(X2)=645.29 cm−1. These constants have been used to calculate X1 and X2 Rydberg–Klein–Rees potentials encompassing energies up to 40% of the dissociation limit. A complete set of hyperfine coupling constants has been determined for the first time and interpreted using appropriate relativistic atomic radial integrals.
Collisionless dissipation of Langmuir turbulence
Authors: Erofeev V. I.
Published: July 2002

An analysis of two experimental observations of Langmuir wave collapse is performed. The corresponding experimental data are shown to give evidence against the collapse. The physical reason for preventing the collapses is found to be the nonresonant electron diffusion in momentums. In this process, plasma thermal electrons are efficiently heated at the expense of wave energy, and intense collisionless wave dissipation takes place. The basic reason of underestimation of this phenomenon in traditional theory is shown to be the substitution of real plasma by a plasma probabilistic ensemble. A theory of nonresonant electron diffusion in a single collisionless plasma is developed. It is shown that corresponding collisionless wave dissipation may arrest spectral energy transfer towards small wave numbers.
Conjectures on the glass transition of polymers in confined geometries
Authors: McCoy John D. , Curro John G.
Published: July 2002

We hypothesize that the shift of the glass transition temperature of polymers in confined geometries can be largely attributed to the inhomogeneous density profile of the liquid. Accordingly, we assume that the glass temperature in the inhomogeneous state can be approximated by the Tg of a corresponding homogeneous, bulk polymer, but at a density equal to the average density of the inhomogeneous system. Simple models based on this hypothesis give results which are in agreement with experimental measurements of the glass transition of confined liquids.
Evolution of host–parasitoid network through homeochaotic dynamics
Authors: Ikegami Takashi , Kaneko Kunihiko
Published: July 2002

Host–parasitoid systems with evolving mutation rates are studied. By increasing the growth rate of hosts, the diversity of both species is maintained dynamically. For the lower growth rate, diversity is brought about by mere parasitism. The average mutation rate for parasites is elevated to a high value, while that for hosts is suppressed at a low level. For the higher growth rate, the mutation rates for both hosts and parasites are elevated to form a symbiotic cluster connected by on-going mutation. This symbiotic state is sustained through a chaotic oscillation keeping some coherency among species. For a flat landscape for hosts, dynamical clustering of oscillation is observed. Lyapunov spectra of such oscillations show that high dimensional chaos with small positive exponents underlies in the symbiotic state. This weak high dimensional chaos, termed ‘‘homeochaos,’’ is essential to the maintenance of symbiosis in ecosystems.
Dependence of thin-film microstructure on deposition rate by means of a computer simulation
Authors: Müller Karl-Heinz
Published: July 2002

A computer simulation is employed to demonstrate, in a two-dimensional growth model, that a vapor-deposited thin film of low adatom mobility undergoes a sudden change from a porous columnar microstructure to a densely packed film if the substrate temperature is increased to a certain value. The temperature where this structural transition occurs is shown to be related to the lower boundary temperature of the empirical structure-zone model. The dependence of the transition temperature and range on the vapor deposition rate is discussed.
Crystal growth of cubic boron nitride by temperature difference method at ∼55 kbar and ∼1800 °C
Authors: Mishima O. , Yamaoka S. , Fukunaga O.
Published: July 2002

The temperature difference method was applied to grow a large single crystal of cubic boron nitride (cBN) under ∼55 kbar and ∼1800 °C using LiCaBN2 as a solvent. The effect of supersaturation of boron and nitrogen atoms in the solvent was studied by changing the temperature difference. The observed difference of the shapes of grown cBN, which varied from a small polyhedral lump to a large hollow crystal, was qualitatively explained by the present understanding of crystal morphology in relation to supersaturation. Conversely, this experimental result suggests that the present understanding of crystal growth by solvent methods at a normal pressure is applicable for growth under very high-pressure and high-temperature conditions. The effect of temperature was also studied, and a cBN single crystal of ∼3 mm in size was obtained by choosing a suitable growth condition.
Permanent-magnet annular, longitudinal field sources
Authors: Clarke John P. , Potenziani II Ernest , Leupold Herbert A.
Published: July 2002

Some high-power millimeter-wave devices need magnetic fields only near the periphery of a cylindrical region in order to focus an electron beam. Some novel periphery of a cylindrical region in order to focus an electron beam. Some novel permanent-magnet configurations are described which can bring about weight savings by providing a cross-sectionally uniform field in an annular region rather than in an entire cyclinder. This is accomplished by an arrangement of axially and radially oriented magnets that allow almost no flux leakage to the environment.
Study of niobium nitrides for superconducting rf cavities
Authors: Fabbricatore P. , Fernandes P. , Gualco G. C. , Merlo F. , Musenich R. , Parodi R.
Published: July 2002

This paper deals with the first results of a study on Nb-N system having as the main goal the performance of niobium nitride rf cavities. The nitrides were obtained by diffusion of nitrogen in bulk niobium at high temperature. Metallurgical and resistive measurements have been done to determine the phases and the critical temperature of the samples. Furthermore, in order to study the rf behavior of the material, a 4.5-GHz niobium nitride cavity has been built and tested. The rf measurements showed, above 4 K, a surface resistance in good agreement with the computed values (1.15 μΩ at 4.2 K), i.e., about a factor of 10 better than the value obtained for niobium at the same temperature and frequency. At temperatures below 4 K, the residual resistance became prevalent, and its value was found to be 0.69 μΩ.
Origin of grain boundary weak links in BaPb1−xBixO3 superconductor
Authors: Takagi T. , Chiang Y.-M. , Roshko A.
Published: July 2002

Although BaPb0.75Bi0.25O3 (BPB) has a comparatively large superconducting coherence length of ∼7 nm and no reported anisotropy in its superconducting parameters, polycrystalline BPB exhibits the same rapid decrease in transport critical current density (Jct) with low applied field (<∼50 Oe) that is characteristic of grain boundary weak links in cuprate superconductors (e.g., La2−xSrxCuO4, YBa2Cu3O7−x ). We have studied the effects of processing thermal history on the formation and morphology of grain boundary phases, and on the composition of BPB boundaries with and without second phase, in order to understand the origin of these weak links. Scanning transmission electron microscopy and Auger electron spectroscopy results show the presence of a Pb-Bi-Ba-O phase that is wetting and liquid above ∼570 °C, but which retracts to three-grain junctions upon slow cooling or annealing at lower temperatures. However, weak-link behavior persists in materials with retracted secondary phase, as well as in hot isostatically pressed samples that never exceed the secondary phase melting temperature. It is found that the grain boundaries remain Bi- and Pb-rich even after the retraction of secondary phases; samples that never exceed the melting temperature of the secondary phase show absence of segregation at some but not all grain boundaries. The composition of the grain boundaries as well as Jct vs temperature measurements indicate that the boundaries act as SIS tunnel junctions.
Effect of surface treatment on SrTiO3: An x-ray photoelectron spectroscopic study
Authors: Nagarkar P. V. , Searson P. C. , Gealy F. D.
Published: July 2002

X-ray photoelectron spectroscopy was used to study the reoxidation kinetics of both mechanically and chemically polished as well as freshly fractured SrTiO3 surfaces. X-ray take-off angles were varied in order to resolve surface contributions from those further into the sample. Most surfaces were found to have Sr/Ti ratios that varied significantly from the stoichiometric ratio of 1. Only the oxygen peaks were found to be take-off angle sensitive. We tentatively identify both adsorbed hydroxyl and carbonate O 1s levels as these angle sensitive peaks, indicating that hydroxyl adsorption occurs very rapidly.
Thermal stresses in double-coated optical fibers at low temperature
Authors: Shiue Sham-Tsong , Lee Sanboh
Published: July 2002

The thermal stresses in double-coated optical fibers at low temperature have been analyzed. The lateral pressure and normal stresses in the glass fiber, primary coating, and secondary coating have been derived. The thermal stresses in the optical fiber are affected by the temperature drop, material properties of the primary and secondary coatings, and their thickness. It is possible to select a suitably polymeric coating to produce minimum lateral pressure in the glass fiber. In order to minimize the thermally induced bending loss, it was found that if the thickness of the polymeric coatings increases, the Young’s modulus of primary coating should increase, but the Young’s modulus of the secondary coating should decrease.
A model of diffusion-limited ice growth inside biological cells during freezing
Authors: Karlsson J. O. M. , Cravalho E. G. , Toner M.
Published: July 2002

A theoretical model for predicting the kinetics of ice crystallization inside cells during cryopreservation was developed, and applied to mouse oocytes, by coupling separate models of (1) water transport across the cell membrane, (2) ice nucleation, and (3) crystal growth. The instantaneous cell volume and cytosol composition during continuous cooling in the presence of glycerol were predicted using the water transport model. Classical nucleation theory was used to predict ice nucleation rates, and a nonisothermal diffusion-limited crystal-growth model was used to compute the resulting crystallization kinetics. The model requires knowledge of the nucleation rate parameters Ω and κ, as well as the viscosity η of a water-NaCl-glycerol solution as a function of both the composition and temperature of the solution. These dependences were estimated from data available in the literature. Cell-specific biophysical parameters were obtained from previous studies on mouse oocytes. A sensitivity analysis showed that the model was most sensitive to the values of κ and η.

The coupled model was used to study the effect of cooling rate and initial glycerol concentration on intracellular crystal growth. The extent of crystallization, as well as the crystal size distribution, were predicted as functions of time. For rapid cooling at low to intermediate glycerol concentrations, the cells crystallized completely, while at high concentrations of glycerol, partial or total vitrification was observed. As expected, the cooling rate necessary for vitrification dropped with increasing glycerol concentration; when cells initially contained ∼7.5 M glycerol, vitrification was achieved independent of cooling rate. For slow cooling protocols, water transport significantly affected the results. At glycerol concentrations greater than ∼3 M, the final intracellular ice content decreased with increasing glycerol concentration at a fixed cooling rate. In this regime, the cooling rate at which a critical amount of ice was formed increased as more glycerol was used. When less than ∼3 M glycerol was initially present in the cell, an increase in glycerol concentration was predicted to cause an increase in the final intracellular ice content at a given cooling rate. In this regime, the critical cooling rate decreased with increasing glycerol concentration. These predictions clarify previous empirical observations of slow freezing phenomena.
Stoichiometry issues in single-crystal lithium tantalate
Authors: Bordui P. F. , Norwood R. G. , Bird C. D. , Carella J. T.
Published: July 2002

Stoichiometry issues in lithium tantalate were studied through Czochralski growth of single crystals and vapor transport equilibration (VTE) of crystalline samples to specified Li/Ta compositions. Crystals were characterized through measurement of the ferroelectric Curie temperature Tc. The VTE experiments indicated a linear variation of Tc with Li/Ta ratio across the investigated range of 47.5–49.5 mol % Li2O. By control of initial melt stoichiometry, crystals representing melt fractions ≳90% were grown having compositional uniformity within ±0.015 mol % Li2O. Growth of the compositionally uniform crystals was determined to take place through incongruent solidification, with lithium rejection from the growth interface compensating for lithium volatilization from the melt surface. With the growth process applied, a melt composition of 48.39 mol % Li2O yielded grown crystals of a uniform 47.85 mol % Li2O solid composition. The lithium tantalate congruent composition was determined to lie at a value less than or equal to 47.70 mol % Li2O.
Magnetic flux penetration process in two-dimensional superconductor covered with ferromagnetic particle array
Authors: Nozaki Yukio , Otani Yoshichika , Runge Katharina , Miyajima Hideki , Pannetier Bernard , Nozières Jean Pierre , Fillion Gerard
Published: July 2002

The magnetostatic effect of a ferromagnetic particle array on an underlying two-dimensional superconducting Nb thin film was investigated in terms of flux penetration processes by means of high sensitive magnetometry. For bare Nb film, a large drop in magnetization due to a flux rearrangement appeared in the low field region below 2.5 mT. However, once magnetic particles were fabricated on the surface of the Nb film, the drop was not observed. In this configuration, the ferromagnetic particles seem to behave as flux guides for the external magnetic field, whereby the flux distribution inside the superconductor is well regulated. Furthermore, a periodical oscillation was observed in the hysteresis loops. This behavior is associated with a flux quantization in the regions where the superconductivity is suppressed by the stray field of the ferromagnetic particles. The local flux density distribution around the ferromagnetic particles was evaluated by using the London equation, and the magnetization curve of the Nb film with periodically modulated superconducting order parameter was calculated.
Electrical resistivity of epitaxial molybdenum films grown by laser ablation deposition
Authors: Malikov I. V. , Mikhailov G. M.
Published: July 2002

The results of electrical resistivity measurements at room and low temperatures, and also of reflection high energy electron diffraction analysis of thin (less than 110 nm) Mo films, grown by laser ablation deposition are presented. The films deposited under ultrahigh vacuum conditions on sapphire (1̄012) substrates at temperatures of 20–750 °C are monocrystalline, with a [001] axis perpendicular to the substrate. It is shown that the ratio of room temperature to residual resistance which characterizes structural perfection, is in the range 12–32 for the films 70 nm thickness. It increases abruptly at film growth temperatures of 200–370 °C and changes weakly at further temperature increase. The analysis of data on the size (thickness) effect of the Mo films deposited at 750 °C revealed that the effective electron mean free path is in the range 0.1–1 μm for the films 15–110 nm thickness. Surface scattering was found to be the basic channel of electron scattering at helium temperatures, with the specular coefficient q∼0.3 and residual bulk electron mean free path ∼100 μm. At low temperatures T<25 K, the temperature dependent part of the resistance is approximated by ρ(T)−ρ0=ATn. The power degree smoothly varies from 3.2 in high quality films deposited at 750 °C, where the effective electron mean free path exceeds film thickness to 4.5 in the films deposited onto cold unannealed substrates, where the effective electron mean free path is comparable with film thickness.
Size selected silicon particles in sol-gel glass by centrifugal processing
Authors: Duval David J. , McCoy Benjamin J. , Risbud Subhash H. , Munir Zuhair A.
Published: July 2002

Centrifugal processing was used to induce size selectivity in Si particles suspended in a silica sol-gel precursor solution. A model was developed to describe Stokes settling of the silicon particles in the sol-gel medium whose viscosity increases exponentially with time eventually leading to hardening to a solid glassy material. An empirical modification to the theoretical model accounts for settling of particle agglomerates. Experimental results for polydisperse silicon particulates centrifuged in a sol-gel of tetraethyl orthosilicate catalyzed by phosphoric acid are reported; the particle size and spatial distribution in the gelled matrix are explained by the model. The utility of centrifugal processing to produce functionally graded materials and semiconductor nanostructures is discussed.
Weighted minimum-norm source estimation of magnetoencephalography utilizing the temporal information of the measured data
Authors: Iwaki Sunao , Ueno Shoogo
Published: July 2002

The weighted minimum-norm estimation (wMNE) is a popular method to obtain the source distribution in the human brain from magneto- and electro- encephalograpic measurements when detailed information about the generator profile is not available. We propose a method to reconstruct current distributions in the human brain based on the wMNE technique with the weighting factors defined by a simplified multiple signal classification (MUSIC) prescanning. In this method, in addition to the conventional depth normalization technique, weighting factors of the wMNE were determined by the cost values previously calculated by a simplified MUSIC scanning which contains the temporal information of the measured data. We performed computer simulations of this method and compared it with the conventional wMNE method. The results show that the proposed method is effective for the reconstruction of the current distributions from noisy data.
Temperature dependence of the domain wall width in LaAlO3
Authors: Chrosch Jutta , Salje Ekhard K. H.
Published: July 2002

Twin wall related diffuse scattering intensities from a single crystal of LaAlO3 were determined using high-resolution x-ray diffraction methods. Rocking curves were measured for sample temperatures between 295 and 900 K. The wall thickness W was determined by comparing the observed diffraction profiles with structure factor calculations for a tanh(x/W) wall profile. It is shown that W≈20 Å at low temperatures and increases slowly with temperature reaching values in excess of 200 Å near Tc≈850 K with W∝|T−Tc|−1.
Masking effect of copper during anisotropic etching of silicon in buffered hydrofluoric acid solutions
Authors: Li Guangming , Jiao Jun , Seraphin Supapan , Raghavan Srini , Jeon Joong S.
Published: July 2002

The etching characteristics of silicon samples of (100) orientation in buffered hydrofluoric acid (BHF) solutions containing different levels of dissolved copper were studied systematically using atomic force microscopy, total reflection x-ray fluorescence, inductively coupled plasma mass spectroscopy and transmission electron microscopy techniques. It was found that the presence of trace amounts of copper ions in BHF solutions can cause not only metallic contamination but also very severe surface roughness. Copper deposits onto the silicon surfaces in the form of submonoatomic layer clusters which act as masks during silicon anisotropic etching in BHF solutions. Surface roughness as high as 12 nm was generated in 30 min of etching in buffered hydrofluoric acid solution containing 100 ppb Cu2+. Cross-sectional TEM micrographs showed that silicon was etched anisotropically in BHF solutions containing Cu2+ ions. Etching rates as high as 1.0 nm/min were obtained on the (100) planes of p-type silicon in the presence of a 100 ppb Cu2+. The size of the etching structures depends on the Cu2+ concentration in solution and the etching time.
Reduction of ice adhesion to stainless steel by ice electrolysis
Authors: Petrenko Victor F. , Qi Suogen
Published: July 2002

We report a very strong and reproducible effect of a small dc bias (−21 to +21 V) on ice adhesion to stainless steel. The effect was found in ice doped with 0.5% NaCl and was absent in very pure ice grown from deionized water. The doping was used to enhance ice electric conductivity. Neither the application of ac voltage nor direct electric heating of the same power as the dc bias caused any noticeable change in ice adhesion. Different physical mechanisms of ice adhesion to metals and possible explanations to the effect are discussed. Generation of electrolytic gases resulting in interfacial cracking is thought to be responsible for the effect.
On standardization of the spin Hamiltonian and the ligand field Hamiltonian for orthorhombic symmetry
Authors: Rudowicz C. , Bramley Richard
Published: July 2002

The idea that the ratio E/D ≡ λ can be confined by a proper choice of the axis system to the range (0,±1/3) serves as a basis for the standardization of the spin Hamiltonian and the ligand field Hamiltonian for orthorhombic symmetry. Due to recent results on the transformation of the Stevens operators Oqk, relations are given which allow for extension of the standardization to the spin Hamiltonian for paramagnetic centers with spin S≥2. Several EPR studies of 3dn and 4 f n ions in crystals are reconsidered. The results prove the usefulness of the clear choice of the parameters Bqk suggested by the standardization idea. Application of the standardization in the area of the ligand field theory, which seems rather novel, is also considered. Crystal-field parameters for several rare earth ions in garnets are recalculated. An arbitrary choice from among the equivalent sets of the crystal-field parameters used in the review by Morrison and Leavitt (1982) should be replaced by a transformation to the ‘‘standard’’ set.
Internal condensation of a polymer molecule induced by saturating bonds
Authors: Tanaka Fumihiko , Ushiki Hideharu
Published: July 2002

This paper discusses the conformational phase change of a macromolecule caused by intramolecular bridging with saturated bonds. We provide a quantitative description of the variation of segment distribution and degree of bond formation among the reactive monomer units when the temperature and the bonding energy are varied. We show that sharp compactization is expected in a good solvent for a polymer chain along which reactive monomers are arranged with wide separation. In the asymptotic regime of high molecular weight M, the mean radius of gyration obeys a scaling law: ∼M0.5 (in good solvent), ∼M0.43 (in theta solvent), and ∼M1/3 (in poor solvent). The results can be intuitively understood by applying the c* theorem holding for a gel.
Valence universal exponential ansatz and the cluster structure of multireference configuration interaction wave function
Authors: Jeziorski Bogumil , Paldus Josef
Published: July 2002

A rigorous algebraic formulation of open-shell coupled-cluster theory is presented. This formulation yields explicit formulas exhibiting the relationship between open-shell cluster amplitudes and linear coefficients of multireference CI wave functions. When the valence-universal exponential ansatz is used, the CI coefficients of states with n valence electrons contribute to the n-body and higher-order cluster operators. The implications of cluster conditions, requiring that the four-body cluster amplitudes be small, are investigated. It is shown that for valence-universal theories these conditions lead to approximate relations involving CI coefficients for states of systems differing in the number of electrons. For Lindgren’s ansatz these relations are linear in the CI coefficients corresponding to states with the largest electron number. For the valence-nonuniversal exponential ansatz of Jeziorski and Monkhorst, the cluster conditions do not mix wave functions for systems which differ in the number of electrons and are formally identical to those of the single-reference coupled-cluster theory. A detailed relationship between the cluster amplitudes of the valence-universal and valence-nonuniversal theories is also derived and discussed.
New approach to Monte Carlo calculation of the free energy: Method of expanded ensembles
Authors: Lyubartsev A. P. , Martsinovski A. A. , Shevkunov S. V. , Vorontsov-Velyaminov P. N.
Published: July 2002

We propose a new effective Monte Carlo (MC) procedure for direct calculation of the free energy in a single MC run. The partition function of the expanded ensemble is introduced including a sum of canonical partition functions with a set of temperatures and additive factors (modification). Random walk in the space of both particle coordinates and temperatures provides calculation of free energy in a wide range of T. The method was applied to a primitive model of electrolyte including the region of low temperatures. In similar way other variants of expanded ensembles are constructed (e.g., over the number of particles N or volume V). Its facilities in quantum statistics (path integral Monte Carlo) and some other applications are also discussed.
Fock space multireference coupled-cluster theory for general single determinant reference functions
Authors: Stanton John F. , Bartlett Rodney J. , Rittby C. Magnus L.
Published: July 2002

The technique of Fock space multireference coupled-cluster (FSMRCC) theory is applied for the first time to problems involving a high-spin open-shell ground state. Explicit spin–orbital equations applicable to any single determinant reference state are presented and some computational aspects of FSMRCC are discussed. The method is illustrated by two applications in which calculations are limited to single and double excitation operators (FSMRCCSD). First, several basis sets and choices of open-shell reference function are used to calculate selected ionization potentials of O2. The FSMRCCSD results obtained with a large generally contracted basis set are uniformly within 0.1 eV of experiment. In addition, FSMRCCSD is applied to a study of symmetry breaking in the 3A2 state of CO2, a classic multireference problem. The force constant for asymmetric distortion is shown to be predicted correctly as positive, unlike ordinary single-reference CCSD which predicts a double-minimum potential. The results of this paper suggest that the open-shell reference FSMRCC approach has wide applicability for the solution of chemical problems, particularly when significant nondynamic electron correlation effects are present.
Application of fractals and kinetic equations to cluster formation
Authors: Villarica M. , Casey M. J. , Goodisman J. , Chaiken J.
Published: July 2002

The log normal distribution is shown to be useful for characterizing cluster distributions produced by coalescence growth mechanisms. The Smoluchowski equation and variations thereof produce cluster size distributions very similar to those produced using nozzle beam expansions and laser chemistry of organometallics. The model provides a statistically unbiased basis for interpreting cluster size distributions produced using a wide variety of synthetic methods. It also provides a unified chemical and physical basis for discussing and rationalizing the results of a wide range of gas phase cluster experiments. Under certain conditions, size distributions can be produced in which there is an alteration in the number of odd and even clusters produced. In addition to some inferences regarding fullerene chemistry, data gleaned from the literature are rationalized on the basis of the kinematics of cluster formation, the fractal dimension of clusters composed of different atoms, the Periodic Table, and the degree to which the translational motion of the coalescing species is diffusional or ballistic.
A multiconfiguration time-dependent Hartree approximation based on natural single-particle states
Authors: Jansen A. P. J.
Published: July 2002

The time-dependent Schrödinger equation is solved with a multiconfiguration form for the state. It is shown that the use of natural single-particle states results in a minimal number of configurations. The equations of motion of the natural single-particle states are derived by differentation with respect to time of the defining equations, which are eigenvalue equations of reduced density matrices. The method is tested on a two-dimensional model of H2 dissociation on a transition metal surface. It is shown that numerically exact solutions can be obtained. Computation times and memory requirements are less than for methods that solve the time-dependent Schrödinger equation directly.
Statistical thermodynamics in the classical molecular dynamics ensemble. III. Numerical results
Authors: Lustig Rolf
Published: July 2002

The statistical thermodynamics of the classical molecular dynamics ensemble [J. Chem. Phys. 100, 3048 (1994); 100, 3060 (1994)] is used in preliminary simulations of systems composed of spherical, linear, and octahedral model molecules. The predicted behavior of general energy and volume derivatives of the classical phase space integrals are shown to hold true. A number-of-particles dependence cannot be detected for any of 12 different thermodynamic properties. It is shown that a curious error compensation makes it impossible to discriminate between two classical choices for W in Boltzmann’s entropy relation S=kB ln W.
The inclusion of connected triple excitations in the equation-of-motion coupled-cluster method
Authors: Watts John D. , Bartlett Rodney J.
Published: July 2002

We report the implementation of connected triple excitations in the equation-of-motion (EOM) coupled-cluster (CC) method for excitation energies for the first time. The reference state is described by the complete CC singles, doubles, and triples (CCSDT) method. Excited states are generated from the reference state wave function by the action of a linear excitation operator including single, double, and triple excitations. The excited state wave functions and energies are obtained by diagonalizing the effective Hamiltonian e−THeT, where T is the cluster operator for the reference state, in the space of singly, doubly, and triply excited determinants. Comparison is made with full configuration interaction excitation energies for several examples (CH+, Be, SiH2, and CH2). These show that EOM-CCSDT is able to describe states which are doubly excited relative to the reference state, as well as singly excited states. Calculations of several excitation energies of BH using an extended basis set are also reported, and show good agreement with experiment.
Vibrational spectra of tetra-atomic silicon–carbon clusters. II. Si2C2 in Ar at 10 K
Authors: Presilla-Márquez J. D. , Gay S. C. , Rittby C. M. L. , Graham W. R. M.
Published: July 2002

Fourier transform infrared measurements on the spectra of the products of the vaporization of silicon/carbon mixtures trapped in solid argon in concert with ab initio calculations using second order many body perturbation theory have resulted in the identification for the first time of two vibrational fundamentals, ν3(b1u)=982.9 and ν4(b2u)=382.2 cm−1, of the rhombic ground state structure of Si2C2. The observed frequencies, intensities, and isotopic shifts are in good agreement with the ab initio predictions. Tentative assignments are also made for fundamentals of the linear (SiCCSi) and distorted trapezoidal isomers. The relative energies of the three isomers have been estimated at various ab initio levels.
The complex mechanical modulus as a structural probe: The case of alkali borate liquids and glasses
Authors: Masnik J. E. , Kieffer J. , Bass J. D.
Published: July 2002

Brillouin light scattering has been used to determine the high-frequency complex mechanical modulus of alkali borate liquids and glasses, as a function of the temperature. The temperature dependence of the complex modulus can be described by an enhanced Maxwell model for linear viscoelastic systems. Accordingly, the module comprises relaxational components and a temperature dependent static modulus, which is determined by the equilibrium volume fraction of kinetically arrested domains. Application of this model to the Brillouin data indicates that the structural relaxations in undercooled glass forming liquids occur via relatively distinct mechanisms, each one becoming thermally activated within a different temperature range. The rate of degradation of the network structure increases with increasing alkali content, and is commensurate of the fragility of the liquid. The structural features which are subject to a change in the context of a particular degradation mechanism are released sequentially, i.e., relaxation, facilitated by the rupture of a given network link, is required before other links of the same type become affected by thermal motion. Mechanisms that are activated at high temperatures involve the diffusional displacements of various atomic species. Immediately above Tg, however, structural relaxations are characterized by the dominance of the bulk viscosity over the shear viscosity, and by positive values of the imaginary part of the complex Poisson ratio. This indicates that, to a significant degree, compressive deformations and head-on collisions between structural moieties are involved in the structural relaxations at these low temperatures. It is surmised that the deformation of boroxol rings, where a boron moves out of the BO3 plane to exchange one of its oxygen neighbors, is underlying to this relaxation mechanism, which results in an increase of the average network ring size.
Response functions in the CC3 iterative triple excitation model
Authors: Christiansen Ove , Koch Henrik , Jo/rgensen Poul
Published: July 2002

The derivation of response functions for coupled cluster models is discussed in a context where approximations can be introduced in the coupled cluster equations. The linear response function is derived for the approximate coupled cluster singles, doubles, and triples model CC3. The linear response functions for the approximate triples models, CCSDT-1a and CCSDT-1b, are obtained as simplifications to the CC3 linear response function. The consequences of these simplifications are discussed for the evaluation of molecular properties, in particular, for excitation energies. Excitation energies obtained from the linear response eigenvalue equation are analyzed in orders of the fluctuation potential. Double replacement dominated excitations are correct through second order in all the triples models mentioned, whereas they are only correct to first order in the coupled cluster singles and doubles model (CCSD). Single replacement dominated excitation energies are correct through third order in CC3, while in CCSDT-1a, CCSDT-1b, and CCSD they are only correct through second order. Calculations of excitation energies are reported for CH+, N2, and C2H4 to illustrate the accuracy that can be obtained in the various triples models. The CH+ results are compared to full configuration interaction results, the C2H4 results are compared with complete active space second order perturbation theory (CASPT2) and experiment, and the N2 results are compared to experiment. Double replacement dominated excitations are improved significantly relative to CCSD in all the triples models mentioned, and is of the same quality in CC3 and CCSDT-1a. The single replacement dominated excitation are close to full configuration interaction results for the CC3 model and significantly improved relative to CCSD. The CCSDT-1 results for the single replacement dominated excitations are not improved compared to CCSD.
Lamellae at a preferential wall
Authors: Pickett G. T.
Published: July 2002

The profile of the interfacial plane of a diblock copolymer layer in its lamellar melt phase when it is brought into contact with a hard, smooth substrate is calculated. The chains are in the strong-stretching limit. Far from the substrate, the planes are perpendicular to the substrate, and they become distorted near it by a small wetting preference for one of the components of the copolymer. The profile of the distortion is calculated in an Alexander model by making an analogy to the steady flow of an incompressible fluid. The contact angle between the two components of the copolymer and the substrate is the same as it would be if the blocks were not joined to make diblock copolymers. The approach to this contact angle is characterized by a singularity which is calculated. For any molecular weight and elasticity asymmetry between the components of the copolymer, the curvature of the interface changes sign contrary to the case of the interface between two simple liquids. For most values of asymmetry, the interface is an exponentially damped oscillation.
A comparison of time- and frequency-domain resonance Raman spectroscopy in triiodide
Authors: Johnson Alan E. , Myers Anne B.
Published: July 2002

A common model for the photodissociative potential surfaces of the triiodide ion in ethanol is used to simulate both the spontaneous resonance Raman (RR) spectra and the femtosecond resonant impulsive stimulated Raman scattering (RISRS) signals for comparison with experimental data. The Fourier transforms of the RISRS signals, while resembling RR spectra, are not the same either theoretically or experimentally, and these differences are only partly due to the finite spectral bandwidth of the pulses in the RISRS experiment. The RISRS signals vary much more strongly with wavelength than do the RR spectra. Direct Fourier transformation of the RISRS signals with a fixed phase tends to diminish the apparent contributions of weaker components due to the different phases of different oscillations. Linear prediction singular value decomposition (LPSVD) is shown to give a more faithful representation of the RISRS power spectra by eliminating the phase problem, but there are still significant differences between the RR and LPSVD-RISRS spectra. Our model, which includes a large number of combination bands between triiodide vibrations and a low frequency solvent or intermolecular mode, gives a good representation of both the experimental RR profiles and the 308 nm RISRS data of Banin et al. [U. Banin, R. Kosloff, and S. Ruhman, Isr. J. Chem. 33, 141 (1993)].