bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective spectroscopy of Pr3+ impurity ions in Y2SiO5, Gd2SiO5, and Lu2SiO5 crystals
Authors: Malyukin Yu. V. , Borisov R. S. , Zhmurin P. N. , Lebedenko A. N. , Grinev B. V. , Znamensky N. V. , Manykin É. A. , Orlov Yu. V. , Petrenko E. A. , Yukina T. G.
Published: July 2002

Based on a study of the low-temperature optical spectra of Pr3+ activator ions in Y2SiO5, Gd2SiO5, and Lu2SiO5 crystals, it is shown that the parameters and character of the crystal-field splitting of the D21 and H43 terms of the impurity ions are substantially different in crystals belonging to different crystallographic types. In Y2SiO5 and Lu2SiO5 crystals a pseudosymmetry effect is observed in the splitting of the D21 term for ions localized in inequivalent cation sites. The activator ions nonuniformly occupy the inequivalent cation sites as their concentration is increased. At high concentrations of activator ions (∼1 at. %) the optical absorption spectra exhibit spectral lines belonging to dimers of activator ions.
Anomalous low-temperature field evaporation and atomic relaxation of the tungsten surface
Authors: Mazilova T. I. , Mikhailovskij I. M. , Wanderka N.
Published: July 2002

The anomalous low-temperature field evaporation of atomic complexes on the (211) face of single-crystal tungsten is investigated by the methods of field ion microscopy. It is shown that as the size of the close-packed atomic islands decreases, the tangential rate of evaporation at 21 K increases by 2–3 orders of magnitude. The experimental results can be used to reveal and investigate atomic relaxation effects at steps on faces with low Miller indices. A method is proposed for determining the subatomic displacements of atoms on the steps as the size of the islands decreases. The observed relaxation effects can be described in a consistent manner in a model of linearly distributed surface forces. The observed size relaxation effect is treated as a response to an increase in the energy of the elastic stresses as the diameter of the atomic islands decreases.
Comparison of high-mode predictive simulations using Mixed Bohm/gyro-Bohm and Multi-Mode (MMM95) transport models
Authors: Hannum David , Bateman Glenn , Kinsey Jon , Kritz Arnold H. , Onjun Thawatchai , Pankin Alexei
Published: July 2002

Two different transport models—the Mixed Bohm/gyro-Bohm [Joint European Torus (JET)] model [Erba et al., Plasma Phys. Controlled Fusion 39, 261 (1997)] and the Multi-Mode model (MMM95) [Bateman et al., Phys. Plasmas 5, 1793 (1998)]—are used in predictive transport simulations of 22 high-mode discharges. Fourteen discharges that include systematic scans in normalized gyroradius (ρ*), plasma pressure (β), collisionality, and isotope mass in the JET tokamak [Rebut et al., Nucl. Fusion 25, 1011 (1985)] and eight discharges that include scans in ρ*, elongation (κ), power, and density in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] are considered. When simulation temperature and density profiles are compared with processed experimental data from the International Profile Database, it is found that the results with either the JET or MMM95 transport model match experimental data about equally well. With either model, the average normalized rms deviation is approximately 10%. In the simulations carried out using the JET model, the component of the model with Bohm scaling (which is proportional to gyroradius) dominates over much of the plasma. In contrast, the MMM95 model has purely gyro-Bohm scaling (proportional to gyroradius squared). In spite of the differences in the underlying scaling of these transport models, both models reproduce the global confinement scalings observed in the scans equally well. These results are explained by changes in profile shapes from one end of each scan to the other. These changes in the profile shapes are caused by changes in boundary conditions, heating and particle source profiles, large scale instabilities, and transport.
Anomalies of the magnon spectrum of a bounded antiferromagnet with a center of antisymmetry. II. Effects of the inhomogeneous exchange interaction
Authors: Tarasenko S. V.
Published: July 2002

By simultaneously taking into account the electric-dipole, magnetic-dipole, and inhomogeneous exchange interactions, it is shown that the spectrum of propagating bulk magnons in a thin-film tetragonal antiferromagnet with a center of antisymmetry can exhibit anomalies that do not exist in either the model of an infinite magnet or in thin films of centrosymmetric antiferromagnets.
H–T
phase diagram of a multilayered Gd/Si/Co film with ferrimagnetic ordering of the layers
Authors: Merenkov D. N. , Chizhik A. B. , Gnatchenko S. L. , Baran M. , Szymczak R. , Vas’kovskiy V. O. , Svalov A. V.
Published: July 2002

The magnetization process of multilayered films [Co(30 Å)/Si(5 Å)/Gd(75 Å)/Si(5 Å)]20 having a ferrimagnetic ordering of the magnetic moments of the cobalt and gadolinium layers and a compensation temperature Tcomp≈118 K is studied by magnetometric and magnetooptical methods. A magnetic-field-induced spin-orientation transition from the collinear to the noncollinear state is observed. The transition field is determined and the H–T magnetic phase diagram is constructed for the multilayered ferrimagnet Gd/Si/Co in the temperature interval 5–140 K. The phase diagram is also calculated in the framework of molecular field theory, and satisfactory agreement with the experimental results is obtained. The constant of the antiferromagnetic exchange interaction between the cobalt and gadolinium layers is established.
Antiferromagnetic impurity states in a semi-infinite ferromagnet for various orientations of the surface relative to the crystal axes
Authors: Petrova T. G.
Published: July 2002

A study is made of spin states localized on an antiferromagnetic impurity found on the surface or in one of subsurface layers of a semi-infinite Heisenberg ferromagnet. Different orientations of the surface relative to the axes of the crystal are considered. The energies and eigenfunctions of the localized impurity states are found as functions of the parameters of the problem. It is found that in the system considered there always exists a definite subsurface layer in which it is energetically most favorable for the impurity to locate. The distance of this layer from the surface is completely determined by the direction of the surface plane relative to the axes of the magnetic lattice.
Simulation of material properties below the Debye temperature: A path-integral molecular dynamics case study of quartz
Authors: Müser Martin H.
Published: July 2002

Classical and path integral molecular dynamics (PIMD) simulations are used to study α and β quartz in a large range of temperatures at zero external stress. PIMD account for quantum fluctuations of atomic vibrations, which can modify material properties at temperatures below the Debye temperature. The difference between classical and quantum mechanical results for bond lengths, bond angles, elastic moduli, and some dynamical properties is calculated and comparison to experimental data is done. Only quantum mechanical simulations are able to reproduce the correct thermomechanical properties below room temperature. It is discussed in how far classical and PIMD simulations can be helpful in constructing improved potential energy surfaces for silica.
Two binary Darboux transformations for the KdV hierarchy with self-consistent sources
Authors: Zeng Yunbo , Ma Wen-Xiu , Shao Yijun
Published: July 2002

Two binary (integral type) Darboux transformations for the KdV hierarchy with self-consistent sources are proposed. In contrast with the Darboux transformation for the KdV hierarchy, one of the two binary Darboux transformations provides non-auto-Bäcklund transformation between two nth KdV equations with self-consistent sources with different degrees. The formula for the m-times repeated binary Darboux transformations are presented. This enables us to construct the N-soliton solution for the KdV hierarchy with self-consistent sources.
The performance of density functional theory for equilibrium molecular properties of symmetry breaking molecules
Authors: Cohen Ryan D. , Sherrill C. David
Published: July 2002

The reliability of density functional theory (DFT) for the prediction of equilibrium molecular properties is assessed for several challenging molecules (F2+, O2+, O2, O4+, F4+, and NO3) which tend to artifactually break spatial symmetry in the Hartree–Fock approximation. DFT appears to be among the more robust methods for such cases, but it is not immune to anomalous property predictions. The BLYP and BPW91 functionals fail dramatically for rectangular O4+ and F4+, where they are unable to find a bound minimum.
Magnetoelastic stresses in rare-earth thin films and superlattices
Authors: Arnaudas J. I. , Ciria M. , de la Fuente C. , Benito L. , del Moral A. , Ward R. C. C. , Wells M. R. , Dufour C. , Dumesnil K. , Mougin A.
Published: July 2002

A study of the magnetoelastic behavior of some rare-earth based thin films and superlattices (SLs) is reported. Magnetoelastic stress (MS) measurements are made by a cantilever capacitive technique over a wide range of temperatures (10–30 K) and magnetic fields (up to 12 T). Expressions are derived which relate the cantilever curvatures and the magnetoelastic stresses in anisotropic thin films and SLs (of cubic symmetry) deposited on crystalline substrates. The magnetoelastic energy associated with the interfaces and the epitaxial stress dependence of the volume MS are investigated by studying the basal plane MS in Hon/Lu15 and Ho10/YmSLs: interface MSs even higher than the volume ones are obtained, and the effect of the epitaxial strain on the bulk MSs is large. The MS contributions are also deduced for Dy/Y and Er/Lu SLs, but for ER/Lu incomplete saturation leads to inconclusive results. Although the latter also happens in Ho/Tm SLs, the effect of the epitaxial strain on the bulk MSs is large. The MS clearly shows anisotropy competition. In TbFe2(t)/YFe2 (1000 Å) (300 Å<t<1300 Å) epitaxial bilayers, all the MS allowed by symmetry the determined, and it is shown that epitaxial stress strongly modifies the tetragonal MS. The thermal dependence of the MS parameters is also analyzed.
A natural decay of mixing algorithm for non-Born–Oppenheimer trajectories
Authors: Hack Michael D. , Truhlar Donald G.
Published: July 2002

We present a new method called the natural decay of mixing (NDM) method for introducing decoherence effects into the semiclassical Ehrenfest self-consistent potential method. The NDM method is similar in spirit to two recently developed methods, the continuous surface switching (CSS) and continuous surface switching II (CSS2) methods, but, like the pure semiclassical Ehrenfest method, it involves only a single variable that serves as both the weight of an electronic state and its electronic population. We demonstrate how this allows the NDM method to be applied to systems where the CSS and CSS2 methods cannot be applied, and also to cases where the CSS and CSS2 methods would be prohibitively expensive. The method is tested for electronically nonadiabatic processes, both reactive and nonreactive, and in a wider context it contributes to the rapidly blossoming fields of quantum measurement and hybrid quantum/classical algorithms for the dynamics of complex systems.
Multichannel quantum defect calculation of the phase lag in the coherent control of HI
Authors: Lefebvre-Brion Hélène , Seideman Tamar , Gordon Robert J.
Published: July 2002

Multichannel quantum defect theory (MQDT) is applied within a unified framework to compute the ionization and dissociation channel phases of HI. Our numerical results illustrate the mathematical origin of a channel phase within the MQDT formalism, and are consistent with the existing theory of this phenomenon, based on the collision formalism and with experimental measurements. The present study explains why previous MQDT calculations predicted that the channel phase vanishes identically.
Model of a two-stage rf plasma reactor for SiC deposition
Authors: Petrov G. M. , Giuliani J. L.
Published: July 2002

A reactor is proposed for plasma-enhanced chemical-vapor deposition of silicon carbide (SiC) at low pressure (∼few Torr). The inductively coupled plasma lies upstream of the growth substrate and serves to dissociate the precursor silane/propane/hydrogen inlet gas. Unlike existing reactors, the design offers the potential for separate control of the temperature in the dissociation region and at the growth substrate. The geometrical parameters and flow conditions appropriate for SiC growth are analyzed with a one-dimensional flow simulation model which includes approximations for lateral diffusive losses to cold walls as well as deposition to the substrate. Twenty-one neutral species and 24 ions are followed with 179 reactions. At 3 Torr, 10 W/cm3, and 300 cm/s inlet flow velocity, the model predicts a growth rate of ∼3 μm/h downstream from the plasma. Negligible ion density exists over the substrate as long as the silane density is sufficiently large due to a feedback process between Si+ and SiH4. Besides heating the gas, the plasma is an efficient source of radical H atoms, which in turn control the abundance of some hydrocarbon species over the substrate. C2H2 is the dominant contributor to the C-bearing flux onto the substrate and the Si atom, which forms by electron reactions, is the most important Si-bearing species. Finally, a sensitive transition in deposition rate is found for the C-bearing species as the power increases from 5 to 10 W/cm3.
Piezoelectric mechanism of orientation of a bilayer Wigner crystal in a GaAs matrix
Authors: Fil D. V.
Published: July 2002

A mechanism for orientation of bilayer classical Wigner crystals in a piezoelectric medium is considered. For the GaAs system the piezoelectric correction to the electrostatic interaction between electrons is calculated. It is shown that taking into account the correction due to the piezoelectric effect leads to a dependence of the total energy of the electron crystal on its orientation with respect to the crystallographic axes of the surrounding matrix. A generalization of Ewald’s method is obtained for calculating the anisotropic interaction between electrons in a Wigner crystal. The method is used to calculate the energy of bilayer Wigner crystals in electron layers parallel to the crystallographic planes (001), (0–11), and (111) as a function of their orientation and the distance between layers, and the energetically most favorable orientation for all types of electron lattices in a bilayer system is found. It is shown that phase transitions between structures with different lattice symmetry in a Wigner crystal can be accompanied by a change of its orientation.
Amplified spontaneous emission in active channel waveguides produced by electron-beam lithography in LiF crystals
Authors: Montereali R. M. , Piccinini M. , Burattini E.
Published: July 2002

In this letter we report the observation of amplified spontaneous emission of the red light from LiF:F2 centers in active channel waveguides realized by electron-beam lithography in lithium fluoride crystals. Low pumping power densities have been used in quasi-continuous-wave regime at room temperature; the appreciable values of the gain coefficients, 4.67 cm−1 with an exciting power density of 0.31 W/cm2 at 458 nm, make this material a good candidate for the realization of active integrated optical devices.
Drag prediction over steep sinusoidal wavy surfaces
Authors: Salvetti M. V. , Damiani R. , Beux F.
Published: July 2002

A parametrization of the form drag due to airflow over sinusoidal wavy surfaces in the presence of significant flow separation is investigated; it is based on a bluff-body analogy. To this aim, the results of large-eddy simulations carried out for various Reynolds numbers and wave slopes are used, together with the data from experiments and other simulations available in the literature. It is shown that, as a first approximation, the drag coefficient may be considered independent of the wave slope and Reynolds number. The value obtained here for rigid sinusoidal waves is close to that computed for wind-ruffled breaking paddle waves.
2√×2√
superstructures and charge transfer in YBa2Cu3O6+x
Authors: Mamalui A. A. , Sablin I. N.
Published: July 2002

Anomalies of the kinetic and thermodynamic properties of YBa2Cu3O6+x (x∼0.9) in the normal state are interpreted as originating from the ordering of oxygen in the (001) CuOx basal planes. A sequence of structural phase transitions is proposed, and the phases are analyzed by the method of static concentration waves. It is shown that the anomalous behavior of the resistivity and the relative elongation of the sample may be due to a charge transfer effect.
Polarization of far-IR radiation from p-type germanium under uniaxial pressure and strong electric field
Authors: Bondar V. , Tomchuk P. , Tulupenko V.
Published: July 2002

Experimental results on the polarization of the far-IR radiation (λ=80–120 μm) from p-type germanium under strong uniaxial pressure in a heating electric field at liquid-helium temperature are reported. The directions of the polarization and electric field are shown to be mainly coaxial for samples under pressure and perpendicular to each other for unstrained samples. The possible reasons for this phenomenon are discussed.
Lower limit on the thermal conductivity of krypton–xenon solid solutions
Authors: Konstantinov V. A. , Revyakin V. P. , Pokhodenko M. A.
Published: July 2002

The isochoric thermal conductivity of the solid solutions Kr1−ξXeξ (ξ=0.14 and 0.37) is investigated in the temperature interval from 80 K to the onset of melting. Its value and temperature dependence are in good agreement with the lower limit of the thermal conductivity of the crystal lattice.
Automated unit for physical research on quantum crystals at millikelvin temperatures
Authors: Ganshin A. N. , Grigor’ev V. N. , Maı̆danov V. A. , Mikhaı̆lov G. A. , Mikheev V. A. , Omelaenko N. F. , Penzev A. A. , Repin V. N. , Rudavskiı̆ É. Ya. , Rybalko A. S. , Tokar’ Yu. A. , Shilin V. A.
Published: July 2002

A cryogenic unit designed for physical research on quantum crystals at ultralow temperatures is described. The unit includes a dilution refrigerator with a hybrid He3 circulation system, an antivibration protection system, and a system of automated control and data acquisition and processing. The construction of the basic units, the thermometry system, the algorithms for measurements, and the software for conducting research on quantum crystals by the method of precision pressure measurements are described. The unit may be used for performing a wide range of tasks in research on various condensed systems at millikelvin temperatures.
Crystal structure and magnetic properties of the compound Nd5Co21B4
Authors: Chu W. G. , Rao G. H. , Yang H. F. , Liu G. Y. , Liang J. K.
Published: July 2002

A compound Nd5Co21B4 belonging to the series Rm+nCo5m+3nB2n with m=3, n=2 has been synthesized by melt spinning. The crystal structure and magnetic properties of the compound have been studied by means of x-ray diffraction and magnetic measurements. The compound crystallizes in a hexagonal structure with space group P6/mmm. The Curie temperature, the saturation moment, and the planar anisotropy field of the compound are 570 K, 31.1 μB/f.u., and 861 kOe, respectively.
Fabrication of highly ordered metallic nanowire arrays by electrodeposition
Authors: Yin A. J. , Li J. , Jian W. , Bennett A. J. , Xu J. M.
Published: July 2002

Highly ordered hexagonal arrays of parallel metallic nanowires (Ni, Bi) with diameters of about 50 nm and lengths up to 50 μm were synthesized by electrodeposition. Hexagonal-close-packed nanochannel anodized aluminum oxide film was used as the deposition template. The deposition was performed in an organic bath of dimethylsulfoxide with metal chloride as the electrolyte. A high degree of ordering and uniformity in these arrays can be obtained with this technique by fine-tuning the electrodeposition parameters. Moreover, an unprecedentedly high level of uniformity and control of the wire length was achieved. The arrays are unique platforms for explorations of collective behavior in coupled mesoscopic systems, and are useful for applications in high-density data storage, field emission displays, and sensors.
Anomalous migration in simulated oscillatory pressure-driven flow of a concentrated suspension
Authors: Morris Jeffrey F.
Published: July 2002

Simulation by Stokesian dynamics of a suspension of noncolloidal spheres flowing in a monolayer channel under the action of a sinusoidally oscillating axial pressure gradient has been performed. The migration behavior is markedly different from the case of a unidirectional pressure-driven flow, where migration is to the centerline. For a range of the characteristic strain undergone by the suspension in a flow half-cycle, denoted S and defined as the mean axial distance traveled by the suspension divided by the channel half-width, particles are found to migrate away from the flow centerline. Strains of 0.1<S<1.5 are found to yield migration toward the walls for φA,bulk=0.4 and the two ratios of channel width (H) to particle radius (a) studied here, H/a=18.3 and H/a=30.5. A particle is found to interact with the same near neighbors throughout the flow when the migration is toward the walls.
Luminescent characteristics of blue-emitting Sr2B5O9Cl: Eu thin-film phosphors
Authors: Hao Jianhua , Cocivera Michael
Published: July 2002

Thin films of Sr2B5O9Cl: Eu were deposited on glass plates using spray pyrolysis of aqueous solutions. Films exhibited blue cathodoluminescence and photoluminescence, indicating the films contained Eu2+ rather than Eu3+. A luminance of 76 cd/m2 at 5 kV was obtained for annealed films on glass substrates. The chromaticity coordinates were x=0.162 and y=0.035 with a dominant wavelength of 450 nm and a 95% color purity.
Magnetooptical studies of the H–T phase diagram of an Fe/Si multilayered film
Authors: Chizhik A. B. , Merenkov D. N. , Gnatchenko S. L. , Fronc K. , Zuberek R.
Published: July 2002

The magnetization reversal of a multilayered Fe/Si film having cubic magnetocrystalline anisotropy is investigated in the temperature interval 25–300 K by magnetooptical methods. It is found that the growth of the biquadratic exchange interaction as the temperature is lowered causes a spontaneous second-order phase transition from a collinear antiferromagnetic state to a noncollinear state. The presence of cubic anisotropy in the film gives rise to spontaneous and magnetic-field-induced first-order phase transitions between noncollinear states. Magnetooptical studies permit constructing the H–T magnetic phase diagram of the multilayered Fe/Si film for an orientation of the external field along the hard magnetization axis [110]. A calculation of the H–T phase diagram in the framework of a model taking into account the bilinear exchange and cubic anisotropy, with constants I1 and K that are assumed to be independent of temperature, and also the biquadratic exchange with a linearly temperature-dependent constant I2. Satisfactory agreement is obtained between the experimental and calculated phase diagrams.
Magnetic properties of irradiated quasi-2D type-II superconductors
Authors: Braverman G. M. , Gredeskul S. A. , Avishai Y.
Published: July 2002

Persistent scaling behavior of magnetization in layered high Tc superconductors with short-range columnar defects is explained within the Ginzburg–Landau theory. In the weak field region, the scaling function differs from that of a clean sample and the critical temperature is renormalized due to defects. In the strong field region, defects are effectively suppressed and the scaling function and critical temperature are the same as in a clean superconductor. This picture is consistent with recent experimental results.
Effects of particle sedimentation and rotation on axisymmetric gravity currents
Authors: Hogg Andrew J. , Ungarish Marius , Huppert Herbert E.
Published: July 2002

The axisymmetric propagation of a relatively dense gravity current of a given initial volume over a horizontal boundary is considered when the intruding fluid is a suspension of heavy particles and the ambient fluid is steadily rotating about a vertical axis. The investigation employs a shallow-water model of the motion. With the introduction of a strained temporal coordinate, it is possible to derive asymptotic expressions for the evolution of the radius and height of the current, the radial and temporal variation of the horizontal velocity, the volume fraction of particles, and the angular velocity. In this way it is possible to distinguish how the Coriolis force and the effects of particle sedimentation inhibit the radial spreading of the flow. The analytical relationships arise directly from the shallow-water equations and thus improve upon previous simple expressions which are based on an a priori prescription of the shape for the current. The analytical results compare favorably with both numerical integration of the full system of equations and experimental data.
Reduction of doping and trap concentrations in 4H–SiC epitaxial layers grown by chemical vapor deposition
Authors: Kimoto Tsunenobu , Nakazawa Satoshi , Hashimoto Koichi , Matsunami Hiroyuki
Published: July 2002

High-purity and thick 4H–SiC(0001) epilayers have been grown by a horizontal hot-wall chemical vapor deposition (CVD) system, which was designed and built at the authors’ group. The background donor concentration has decreased by reducing pressure during CVD, and a low donor concentration of 1–3×1013 cm−3 was achieved by CVD growth at 80 Torr. The free exciton peaks dominated in low- and room-temperature photoluminescence spectra without titanium or point-defect related peaks. The electron mobility reaches 981 cm2/V s at room temperature and 46 200 cm2/V s at 42 K. The total trap concentration could be reduced to 4.7×1011 cm−3 by increasing the input C/Si ratio.
Excitonic luminescence in the drift of excess electrons through liquid and solid rare gases
Authors: Gordon E. B. , Shestakov A. F.
Published: July 2002

It is shown that the excitation of electronic states is the main channel of energy loss of excess electrons drifting in moderate (⩾103 V/cm) electric fields through condensed heavy rare gases (Rg). These losses, together with scattering on resonances of metastable negative ions (Rg*)−, determine the dependence of the average energy of the electrons and their drift velocity vd on the electric field E both in condensed Rg and in dense gases. In particular, explanations are given for the constancy of vd at large E and for the transformation of the electroluminescence spectrum upon changes in the density of heavy particles and their temperature. Thus it is predicted that localized excitons can be efficiently excited in the bulk of crystalline and liquid Xe, Kr, and Ar, with a yield of around 102 excitons (and UV photons) per electron.
Ionization and hydrolysis of dinitrogen pentoxide in low-temperature solids
Authors: Agreiter J. , Frankowski M. , Bondybey V. E.
Published: July 2002

Solid layers of interest for the chemistry of polar stratospheric clouds are investigated. Mixtures of covalent N2O5 and water in various molar ratios are deposited from the vapor phase on a cold 12 K substrate. By repeatedly recording Fourier transform infrared spectra of the samples during gradual warmup to 200 K over a period of several hours the hydrolysis process can be followed. At each concentration the process is found to proceed in several distinct steps with sharp temperature thresholds. In samples containing only small amounts of water the covalent N2O5 is first, at around 110 K, converted to an ionic nitronium nitrate, and only in a subsequent step does NO2+NO3− react to form nitric acid.
Precise analysis of frequency domain photon migration measurement for characterization of concentrated colloidal suspensions
Authors: Sun Zhigang , Huang Yingqing , Sevick-Muraca Eva M.
Published: July 2002

Frequency domain photon migration (FDPM) is a new method for characterization of concentrated colloidal suspensions using multiply scattered light. The ability of FDPM to determine size and interaction characteristics of the particulate phase of colloidal suspensions depends largely upon the accuracy and precision of FDPM-measured optical properties. In this work, FDPM measurements at multiple modulation frequencies and multiple source-to-detector distances are systematically analyzed for obtaining accurate and precise scattering properties of colloidal suspensions. Two different data analysis methods, multifrequency (MF) nonlinear regression and multidistance (MD) linear regression, and corresponding various strategies for fitting to the optical diffusion equation are investigated. The accuracy and precision of estimated scattering coefficients by different approaches are compared. Results show that MD linear regression with simultaneous regression of average intensity and phase shift or amplitude and phase shift data provides the best data analysis method since it provides not only accurate estimated parameters but also an accurate estimation of their uncertainties. Finally, an important criterion, derived from the photon diffusion model, is proposed for checking the consistency of measurement data and optimizing experimental conditions for FDPM characterization of multiply scattering materials.
Surface-bulk hybrid mode in 36°-rotated YX cut of lithium tantalate with periodic metal grating
Authors: Naumenko N. F. , Abbott B. P.
Published: July 2002

We report on a surface-bulk hybrid acoustic mode, which exists within a limited frequency interval in some piezoelectric substrates within a periodic metal grating. These hybrid modes result from the coupling between a bulk wave and a counter-propagating surface (or leaky) wave. An example of such a hybrid mode, which propagates in 36°-YX cut of lithium tantalate, is described. The hybrid mode gives rise to an additional branch of dispersion relation. The Bragg reflection stop band occurs due to phase match between surface and bulk waves. The lower edge of this stop band manifests itself by a resonance of harmonic admittance, being a reason of undesired resonances in resonator filters.
Self-consistent calculation of the spectrum of quasiparticles in a superfluid Bose liquid with a quenched Bose–Einstein condensate
Authors: Pashitskiı̆ É. A. , Vilchinsky S. I. , Mashkevich S. V.
Published: July 2002

An iterative method is used in a self-consistent calculation, at T=0, of the normal Σ11 and anomalous Σ12 self-energy parts, the boson polarization operator Π on the “mass shell,” and the quasiparticle spectrum E(p) in a superfluid Bose liquid with an interaction-quenched single-particle Bose–Einstein condensate (BEC). The calculation is based on a system of “truncated” integral equations for Σ11 and Σ12 with allowance for terms of first order in the density n0/n≪1 of the BEC and with the “bare” interaction between bosons taken in the form of the repulsive pseudopotential in the “semitransparent spheres” model, for which the Fourier component of the pseudopotential is an oscillatory sign-varying function of the momentum transfer. By fitting with a single adjustable parameter—the amplitude of the initial repulsive pseudopotential—one can achieve completely satisfactory agreement of the theoretical quasiparticle spectrum E(p) with the measured spectrum of elementary excitations in superfluid helium from neutron-scattering experiments over a wide momentum range (0⩽p⩽pmax≃4 Å−1).
Magnetic properties and microstructure of LaCo5-based powders produced by mechanical milling and subsequent annealing
Authors: Okumura H. , Zhang F. , Hadjipanayis G. C.
Published: July 2002

The magnetic and structural properties of LaCo5-based LaxCo100−x (x=17–22) alloys have been studied in powders synthesized by mechanical milling and subsequent annealing. A record high coercivity (over 1.7 T) with a Mr/Ms ratio about 0.7 (measured at room temperature) has been obtained in La22Co78 powders. Their microstructure consists of major LaCo5 phase grains with the grain size of about 150–350 nm, coexisting with LaCo13 phase particles (30–70 nm) and La/La oxide grains (100–200 nm). The observed magnetic properties originate from the high anisotropy field and uniform grain size and shape of the LaCo5 phase. The demagnetization curve, however, often exhibits a shoulder, which was correlated with the appearance of the magnetically soft 1:13 phase and with the inhomogeneity in the microstructure. All the analyses are consistent with a nucleation-type LaCo5 magnet, where the coercivity is attributed to the difficulty in the formation of reversed magnetic domains. The observed phases and microstructure are briefly discussed based on a possible nonequilibrium phase transition resulting in chemical inhomogeneity and oxidation.
Infrared spectra of thin films of cryocondensates of an isotopic water mixture
Authors: Aldijarov A. , Drobyshev A. , Sarsembinov S.
Published: July 2002

The spectral characteristics of thin films of vacuum condensates of an isotopic water mixture consisting of 10% H2O, 50% HDO, and 40% D2O are investigated. The cryocondensates are obtained on a metallic mirror at a temperature of 30 K and a pressure of the gas phase over the substrate during the cryodeposition of 6.7×10−4 Pa. The IR spectra are investigated in the frequency range 4200–400 cm−1 for films of different thicknesses (d=0.1–2.5 μm). It is found that the increasing thickness of the water film during the course of the condensation leads to substantial changes in the spectral reflectivity in the range of characteristic frequencies of the intramolecular vibrations—an increase in the absorption intensity and in the width of the spectral bands. It is found that for d⩾2.5 μm a film of water cryocondensate is optically transparent over a wide spectral interval.
Edge harmonic oscillations produced by toroidal velocity shear
Authors: McCarthy D. R.
Published: July 2002

It is shown that, for a plasma with similar edge density and parallel velocity profiles to that of the Doublet III-D [Fusion Technol. 8, 441 (1985)] tokamak operating in the quiescent double barrier (QDB) regime, the system is unstable to the parallel velocity shear instability. By means of three-dimensional nonlinear simulations, it is found that this system produces turbulence that is radially localized in the vicinity of the parallel velocity gradient and has a toroidal structure. These results are similar to the edge harmonic oscillations (EHOs) that are observed during the QDB discharge. Previously, it was thought that the EHOs were due to a magnetic magnetohydrodynamic mode, yet such structures have not been observed in any one-fluid theoretical models. These results indicate that EHOs may be due to this instability, which can only be realized in a two fluid model.
On the role of Jahn–Teller vibrations in the mechanism of high-Tc superconductivity of intercalated C60 fullerite films with p-type conductivity
Authors: Loktev V. M. , Pashitskiı̆ É. A.
Published: July 2002

An attempt is made to explain the high values of the superconducting transition temperature observed in intercalated fullerite films. The approach is based on the fact that charged C60 molecules in hexagonal lattices have degenerate electronic terms which are strongly coupled to the Jahn–Teller intramolecular vibrations. Certain other effects leading to enhancement of the superconductivity in molecular metals are also discussed.
Synthesis of boron nitride nanowires
Authors: Huo K. F. , Hu Z. , Chen F. , Fu J. J. , Chen Y. , Liu B. H. , Ding J. , Dong Z. L. , White T.
Published: July 2002

A chemical method has been developed for synthesizing boron nitride nanowires through the reaction of a mixture gas of nitrogen (N2) and ammonia (NH3) over nanoscale α-FeB particles at 1100 °C. Boron content in the product comes from the α-FeB catalyst itself. Transmission electron microscopic image indicates an abundant quantity of BN nanowires with diameter about 20 nm and length up to several tens of microns. The product has also been characterized by high-resolution electron microscopy and electron energy loss spectrometer. The perfectly straight lattice fringes with an interlayer spacing of about 0.333 nm corresponding to d0002 spacing of h-BN indicate that the BN nanowires are well crystallized. Also, a growth mechanism has been speculated.
Aging effect on the magnetic and transport properties of laser-deposited La0.5Sr0.5CoO3−δ films
Authors: Prokhorov V. G. , Kaminskiĭ G. G. , Ishchuk V. M. , Chukanova I. N. , Lee Y. P. , Kim K. W.
Published: July 2002

Magnetic and transport studies are carried out on laser-deposited films of La0.5Sr0.5CoO3−δ and La0.65Sr0.35CoO3. It is shown that prolonged aging (for up to one year) of La0.5Sr0.5CoO3−δ films leads to a decrease of the oxygen concentration to a deficit δ≈0.08. The oxygen deficit that forms is accompanied not only by a redistribution of the charge between the cobalt ions of different valences but also by the formation of topological disorder in the Co–O–Co conducting channel as a result of the accumulation of oxygen vacancies. The observed growth of the resistivity with decreasing temperature is more accurately described in a model of weak localization of the carriers than by a thermally activated conduction mechanism. In addition to the usual ferromagnetic transition at TC≈240 K, in the “aged” La0.5Sr0.5CoO2.92 film an additional transition, typical of a magnetic transition in a spin glass, is observed at TM≈50 K. Analysis of the temperature behavior of the resistivity of La0.5Sr0.5CoO3 and La0.65Sr0.35CoO3 films found in the metallic state show that in addition to the quadratic term proportional to T2, the temperature dependence of the resistivity contains an exponential term of the form ∝exp(−T0/T), which is due to the opening of a spin gap in the conducting channel at low temperatures.
Statistical measures derived from the correlation integrals of physiological time series
Authors: Ivanov D. K. , Posch H. A. , Stumpf Ch.
Published: July 2002

In this work correlation integrals are used for the analysis of various EEG signals from rabbits in resting states and under the influence of an anesthetic. The comparison with surrogate data reveals nonlinear dynamics in all of the time series. Our attempt to determine the correlation dimension D2 by the modified algorithm of Theiler [Phys. Rev. A 34, 2427 (1986)] failed since no saturation is reached with increasing embedding dimension. The hypothesis of low-dimensional chaos turns out to be inconsistent with our results, but we can still distinguish, at least qualitatively, between different states of brain dynamics. A quantitative characterization of the time series is possible by defining correlation parameters Pa derived from correlation integrals reflecting also autocorrelation of the signal.
Reflection and refraction of optical beams at dielectric interfaces
Authors: Regan Jeffery J. , Andersen David R.
Published: July 2002

The phenomena associated with the reflection and refraction of light have been widely studied. As the level of dimensionality of the model used in the analysis increases, so does the variety of interesting phenomena that emerge from the analysis. For example, plane-wave calculations give rise to Brewster angle and total internal reflection effects. If a finite two-dimensional slab beam is considered, Goos-Hänchen, focal, and angular shifts become apparent. As the problem is generalized to higher dimensions, possibly including the temporal dimension, additional phenomena may be expected as well. This paper begins by defining the terms and general notation used with the interface problem by reviewing plane-wave (infinite field) solutions. This is followed by a literature review of some two-dimensional results, including a discussion of the Goos-Hänchen, focal, and angular shift. Then numerical solutions to the full three-dimensional problem of finite beams (under a paraxial approximation) are presented using modern visualization techniques. The numerical results provide an intuitive understanding of the interface phenomena from a new perspective, graphically underscoring the difference between the geometrical ray model of reflection and refraction and the complicated field interaction that actually occurs. Finally, the numerical model is extended to include results for the nonlinear interface.
Film formation mechanisms in the plasma deposition of hydrogenated amorphous silicon
Authors: Tsai C. C. , Knights J. C. , Chang G. , Wacker B.
Published: July 2002

By studying the step coverage of plasma-deposited amorphous silicon and germanium on patterned substrates, we find that the film formation process under device-quality deposition conditions has a substantial component that behaves like a surface rate-limited chemical vapor deposition process, while conditions producing defective material are associated with a much more physical-vapor-deposition-like process. An explanation involving surface reactions of SiHx radicals is proposed.
Electroreflectance of silver in smooth and microstructured tunnel junctions
Authors: Goudonnet J. P. , Dufour J. P. , Niquet G. , Chabrier G. , Vernier P. , James D. R.
Published: July 2002

Measurements of the electroreflectance (ER) of smooth and microstructured Ag surfaces have been performed with use of Al-Al2O3-Ag tunnel junctions at room temperature. The ER spectra of smooth silver are found to be in excellent agreement with those reported earlier by Kolb and Kotz [Surf. Sci. 24, 417 (1971)] in electrochemical cells. A dip at hν=3.78 eV can be seen for p polarization and a peak appears at hν=2.94 eV due to the surface plasmon excited at the Al-Al2O3 interface. In the microstructured junctions the very high field (∼1010 V/cm) present at the top of the Ag posts induces a shift of the maximum at 3.9 eV for p polarization and a large negative signal in the 3–4 eV range which cannot be observed in the conventional ER experiments. The free-electronlike theory of the ERs does not account for these experimental data.
Magnetic properties and microstructure of magnesium-doped Nd-Fe-B magnets
Authors: Lin C. H. , Chen S. K. , Lin K. D. , Chang W. C. , Chin T. S.
Published: July 2002

A number of Nd15 Fe79−x Mgx B6 magnets with x up to 0.41 and pseudoternary Nd2(Fe1−yMgy)14B compounds with y up to 0.081 have been prepared by conventional powder metallurgy processes. Magnetic measurements indicate that for the magnet alloys i Hc increases as x increases up to 0.25 without a loss in Br, hence the (BH)max values are slightly enhanced. The maximum increase in i Hc is about 15% for x=0.25. Extensive Mg-rich precipitates inside the Nd-rich phase have been observed by electron probe microanalysis (EPMA). Higher Mg intensity at grain boundaries is also detected by EPMA. The reasons for the i Hc increase might be the grain boundary cleaning ability of Mg dopant. For the pseudoternary compounds, the anisotropy field HA is found to increase only slightly due to Mg doping while TC remains practically unchanged.
Electrical noise measurements on magnetic films (invited)
Authors: Weissman M. B. , Israeloff N. E.
Published: July 2002

The magnetic structure and dynamics of thin films, especially antiferromagnets and spin glasses, are notoriously difficult to study due to the small volumes of materials involved. Electrical resistivity turns out to be sensitive to small fluctuations in magnetic configurations, allowing measurements of magnetic dynamics in films. Since measurements can be made in extremely small samples, the properties of individual fluctuating units, such as antiferromagnetic domains, can be studied directly. We discuss results in the antiferromagnet Cr and the spin glass CuMn.
Nonuniformity in amorphous ribbon delay lines after stress and current annealing
Authors: Hristoforou E. , Reilly R. E.
Published: July 2002

Experimental results concerning the reduction of the amplitude nonuniformity of a Metglas 2605SC magnetostrictive delay line (MDL) after stress relief and current annealing under stress are reported. Nonuniformity is defined here as the fluctuation of the peak voltage V0 received by a coil around the MDL at a fixed position versus the distance between the coil and the point of excitation by a pulsed magnetic field, under uniform conditions of bias field and geometry along the length of the MDL. Stress-relieved delay lines were subjected to stress and current annealing. The results show that the fluctuation function was improved for a stress-relieved MDL, subjected to 200 N/mm2 stress and 300 m amps dc longitudinal annealing current. It was also observed that the normalized relationship for V0 versus the exciting pulsed current is the same for any point of excitation under uniform conditions of dc bias field. This could be used to simplify a computational correction of the nonuniformity function.
Experimental study of correspondence between the electron distribution function in plasma and the second derivative of the Langmuir probe I-V characteristic
Authors: Shun’ko E. V.
Published: July 2002

Experimental results are presented that were obtained in a glow discharge in coaxial geometry. Crossed E and H fields in the gas mixture of 0.8 Torr CO2+2.2 Torr N2+5 Torr He were used. A calculation was made of the radiation power P of a gas-discharge laser (utilizing the studied plasma as the active element) on the basis of the measured probe’s I-V characteristics. The calculated dependence P(H) agrees with the results of direct calorimetric measurements. This agreement verifies that the second derivative of a Langmuir probe I-V characteristic varies in the same way as the distribution function of plasma electrons.
Peculiar magnetic property of pyrolytic carbon prepared from adamantane
Authors: Tanaka Kazuyoshi , Kobashi Masahiro , Sanekata Hideki , Takata Akira , Yamabe Tokio , Mizogami Shigeyoshi , Kawabata Kazushige , Yamauchi Jun
Published: July 2002

Magnetic-property measurements of pyrolytic carbon prepared by the thermal chemical vapor deposition of adamantane were carried out using the Faraday balance method and the electron-spin-resonance (ESR) spectroscopy. Two kinds of samples under different preparation batches were employed to examine the batch dependence as well as the magnetic properties of each. The content of ferromagnetic metallic oxide as impurity in these samples has been confirmed to be low enough not to influence the present magnetic-property measurements. Analysis of the magnetization curves observed in the magnetic field range 0–5 T has shown that these samples are basically superparamagnetic and, even, ferromagnetic at low temperature in one sample. The ESR measurements have also supported these aspects. The connection of the magnetic properties and batch dependence obtained here will be discussed in detail.
Dielectric properties of gold-containing plasma-polymerized thin films
Authors: Canet P. , Laurent C. , Akinnifesi J. , Despax B.
Published: July 2002

Electrical properties of gold-containing plasma-polymerized thin films have been studied in the dielectric regime (isolated conducting clusters dispersed in a polymeric matrix). dc measurements over a wide temperature range provide evidence for a transport process involving the matrix itself as opposed to tunneling directly across the insulating barrier between metallic clusters. The films display space-charge-limited conduction which is due to the existence of trap states in the polymeric phase. An exponential distribution of traps with a peak value of the order of 1017 cm−3 eV−1 has been deduced from the voltage-current data. The ac behavior is dominated by conduction losses at low frequency with a dissipation peak due to interfacial polarization between metal and matrix in the kHz range. Another relaxation is found for gold-rich films. The full interpretation requires more details on the polymeric phase which composition and electrical properties change gradually with an increasing gold concentration.