bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure development during chaotic mixing in the journal bearing flow
Authors: Galaktionov O. S. , Anderson P. D. , Peters G. W. M.
Published: September 2002

Laminar mixing in the two-dimensional time-periodic Stokes flows between eccentric cylinders [journal bearing flow (JBF)] is studied using the extended mapping method [Galaktionov et al., Int. J. Multiphase Flows 28, 497 (2002)] with the emphasis on the material stretching, e.g., the interface generation abilities, of the flow. With this flexible and computational advantageous method both, the macroscopic material transport and the evolution of the microstructure can be described. It enables a convenient way for studying the material stretching in the flow and moreover, it provides spatial distribution of locally averaged stretching values instead of pointwise statistics, which was typical for previous studies [Liu et al., AIChE J. 40, 1273 (1994); Muzzio et al., Phys. Fluids A 3, 822 (1991)]. The results clearly indicate how the total amount of stretching generated by the flow depends on the parameters of the flow protocol, and that this is not just proportional to the work done on the system, as was suggested earlier in Muzzio et al., Phys. Fluids A 3, 822 (1991). It was found that when self-similar patterns are established, distinctive zones in the flow, which we call “microstructural demixing zones,” are observed, where interfaces are contracted during a typical period of the mixing process. Spatial nonuniformity of stretching in chaotic flows calls for additional mixing measures that reflect the nonuniformity of self-similar stretching patterns, created by time-periodic mixing flows.
Nova indirect drive Rayleigh–Taylor experiments with beryllium
Authors: Marinak M. M. , Glendinning S. G. , Wallace R. J. , Remington B. A. , Weber S. V. , Haan S. W. , Collins G. W.
Published: September 2002

The growth due to the Rayleigh–Taylor (RT) instability of single-wavelength surface perturbations on planar foils of copper-doped beryllium [BeCu] was measured. These foils were accelerated by x-ray ablation, with a shaped drive designed to produce ∼1.5 ns of uniform acceleration. A range of wavelengths (λ=30–70 μm) was used with initial amplitudes η0/λ=0.03–0.04. Tabulated opacities from detailed atomic physics models, HOPE [J. Quant. Spectros. Radiat. Transf. 43, 381 (1990)], OPAL [Astrophys. J. 397, 717 (1992)] and super transition array (STA) [Phys. Rev. A 40, 3183 (1989)] were employed in simulations. Other ingredients which can affect modeling, such as changes in the equation of state and the radiation drive spectrum, were also examined. This calculational model agrees with the Nova single wavelength RT perturbation growth data for the BeCu. No adjustments to the modelling parameters were necessary.
Degenerate perturbation theory corrections for the vibrational self-consistent field approximation: Method and applications
Authors: Matsunaga Nikita , Chaban Galina M. , Gerber R. Benny
Published: September 2002

A new algorithm for computing anharmonic vibrational states for polyatomic molecules is proposed. The algorithm starts with the vibrational self-consistent field (VSCF) method and uses degenerate perturbation theory to correct for effects of correlation between different vibrational modes. The algorithm is developed in a version that computes the anharmonic vibrational spectroscopy directly from potential energy surface points calculated by using ab initio codes. The method is applied to several molecules where near degeneracies occur for excited vibrational states, including HOOH, HSSH, and HOOOH. The method yields results in very good accordance with experiments and generally provides improvements over nondegenerate perturbation corrections for VSCF.
Optical properties of Zn1−xMnxTe epilayers grown by molecular beam epitaxy
Authors: Shih Y. T. , Chiang W. C. , Yang C. S. , Kuo M. C. , Chou W. C.
Published: September 2002

Zn 1−x Mn x Te  (0⩽x⩽0.268) epilayers were grown on GaAs(001) substrates by molecular beam epitaxy. The optical properties of the epilayers were studied using reflectivity, transmission, and photoluminescence (PL) measurements. The energy gaps of the epilayers were found to increase linearly with Mn concentration. From the PL spectra, a redshift of the PL peaks was observed as the temperature was increased. The exciton activation energies of the epilayers were determined by the plots of logarithmic-integrated PL intensity versus inverse temperature. Accordingly, they increase with Mn concentration. The Varshni and O’Donnell relations, which mimic the temperature dependence of semiconductor energy gaps were used to fit the experimental data [Y. P. Varshni, Physica 34, 149 (1967); R. P. O’Donnell and X. Chen, Appl. Phys. Lett. 58, 2924 (1991)]. Good fits were obtained by both relations. From the fitted results, the entropy of formation of electron–hole pairs in the Zn1−xMnxTe epilayers at room temperature was estimated to be roughly 0.5 meV/K.
Thermally induced modifications on bonding configuration and density of defects of plasma deposited SiOx:H films
Authors: San Andrés E. , del Prado A. , Mártil I. , González-Dı́az G. , Bravo D. , López F. J.
Published: September 2002

The bonding configuration, hydrogen evolution, and defect content of rapid thermally annealed (RTA) SiOx:H films of different compositions were studied. Infrared absorption measurements showed that all the hydrogen present in the films is lost at annealing temperatures below 600 °C without any change in the oxygen to silicon ratio of the films. The activation energy of the hydrogen release is in the 0.21–0.41 eV range independently of film composition, suggesting that the process occurs via network bond reactions. For annealing temperatures higher than 700 °C, a change in the Si–O–Si stretching wave number from the initial unannealed value to the 1070–1080 cm−1 range was promoted, independently of the initial film composition. Electron spin resonance measurements showed that all the films contain two type of bulk paramagnetic defects: the E′ center (•Si≡O3) and the silicon dangling bond center (•Si≡Si3). The RTA process promotes a general decrease of defect concentration for annealing temperatures below 400 °C. At higher temperatures, E′ center disappears, and the •Si≡Si3 center increases its concentration up to the 1017–1018 cm−3 range. This suggests that the RTA at higher temperatures promotes the formation of a high-quality, almost defect-free, SiO2 matrix in which highly defective Si nanocrystals are also formed, where the •Si≡Si3 centers are located.
Phase transition and dielectric properties of La-doped Pb(Zr,Sn,Ti)O3 antiferroelectric ceramics under hydrostatic pressure and temperature
Authors: Xu Zhuo , Feng Yujen , Zheng Shuguang , Jin An , Wang Fanglin , Yao Xi
Published: September 2002

Phase transition and dielectric properties of La-doped Pb(Zr,Sn,Ti)O3 antiferroelectric ceramics under hydrostatic pressure and temperature have been studied, and effects of temperature on the pressure-induced phase transition and the dielectric property dependence on the applied hydrostatic pressure have been investigated. It has been found from experimental results that the ferroelectric–antiferroelectric phase transition pressure is decreased with increasing temperature, and that when applying hydrostatic pressure the ferroelectric–antiferroelectric phase transition temperature is decreased and antiferroelectric–paraelectric phase transition temperature is increased. All these observed phenomena are very useful and informative for deep understanding of the behaviors of temperature and pressure-induced dielectric frequency dispersion and diffuse phase transition.
Positive dielectrophoresis and heterogeneous aggregation in high-gradient ac electric fields
Authors: Qiu Zhiyong , Markarian Nikolai , Khusid Boris , Acrivos Andreas
Published: September 2002

Experiments were conducted in a parallel-plate channel in which an extremely dilute suspension of heavy, positively polarized spheres was exposed to an ac electric field under conditions such that the field lines were arranged in the channel cross section perpendicular to the streamlines of the main flow. To reduce the effects of the gravitational settling of the particles, the channel was slowly rotated around a horizontal axis. Following the application of a high-gradient strong ac field (∼ several kV/mm), the particles were found to move towards both the high-voltage and grounded electrodes and to form arrays of “bristles” along their edges. The process was also modeled theoretically by computing the trajectories of individual particles under the action of dielectrophoretic, viscous, and gravitational forces and under conditions of negligibly small particle Reynolds numbers. The model calculations required no fitting parameters because the particle polarizability was determined independently by measuring the frequency and concentration dependence of the complex dielectric permittivity of a suspension in a low-strength field (∼ V/mm). The predictions of this model were found to be consistent with the experimental data for the rate of particle accumulation on the electrodes but not for the aggregation pattern which, even for initially extremely dilute suspensions, appeared to be governed by the interparticle interactions and to be created by a two-step mechanism. The results of our studies provide the basic characteristics of the field-induced particle motions and segregation needed for the design and optimization of electrohydrodynamic apparatuses.
Studies of polymer conformation and dynamics in two dimensions using simulations based on the Dynamic Lattice Liquid (DLL) model
Authors: Polanowski Piotr , Pakula Tadeusz
Published: September 2002

The Dynamic Lattice Liquid (DLL) model has been implemented as a simulation algorithm for two-dimensional (2-D) polymeric systems. The model can work with density factor ρ=1 and became a basis for a parallel algorithm, which takes into account coincidences of elementary molecular motion attempts resulting in local cooperative structural transformations. Systematic studies of athermal polymer systems on the two-dimensional triangular lattice are presented for various concentrations of linear polymers with respect to an explicitly considered solvent. Both static and dynamic properties are characterized. The simulation results reflect molecular packing and other properties of monomolecular polymer layers, which can be relevant to these obtained in some thin film formation techniques.
Weakly nonlinear nonaxisymmetric oscillations of capillary bridges at small viscosity
Authors: Higuera Marı́a , Nicolás José A. , Vega José M.
Published: September 2002

Weakly nonlinear nonaxisymmetric oscillations of a capillary bridge are considered in the limit of small viscosity. The supporting disks of the liquid bridge are subjected to small amplitude mechanical vibrations with a frequency that is close to a natural frequency. A set of equations is derived for accounting the slow dynamics of the capillary bridge. These equations describe the coupled evolution of two counter-rotating capillary waves and an associated streaming flow. Our derivation shows that the effect of the streaming flow on the capillary waves cannot be a priori ignored because it arises at the same order as the leading (cubic) nonlinearity. The system obtained is simplified, then analyzed both analytically and numerically to provide qualitative predictions of both the relevant large time dynamics and the role of the streaming flow. The case of parametric forcing at a frequency near twice a natural frequency is also considered.
Electric-field tuning of the Rabi splitting in a superlattice-embedded microcavity
Authors: Dickerson J. H. , Son J. K. , Mendez E. E. , Allerman A. A.
Published: September 2002

We have demonstrated comprehensive electric field tuning of the Rabi splitting between the excitonic and photonic modes of a superlattice-embedded microcavity. Using photocurrent spectroscopy to measure the coupling between the modes, we have tuned the microcavity to the maximum possible splitting. We have observed a marked increase in the splitting from 4.5 to 11.5 meV, due to the electric-field enhancement of the superlattice exciton’s oscillator strength and the oscillator strength’s subsequent decrease due to the quantum confined Stark effect. As well, we have determined the oscillator strength for the exciton, finding good agreement with theoretical and experimental values.
Experimental investigation of flyer character driven by a laser and increasing pressure with the flyer technique
Authors: Fu Sizu , Gu Yuan , Huang Xiuguang , Wu Jiang , He Juhua , Ma Mingxun , Luo Pingqing , Zhang Yonghui
Published: September 2002

Using a special flyer-inclined target, the dynamic characters of a flyer were investigated experimentally for the first time. On the basis of the observation of the shock luminescent signal from the rear surface of a target impacted continuously by the flyer, it appears that the flyer has a steady flying velocity of ∼30.3 km/s after flying a distance longer than ∼30 μm at irradiance of ∼0.8×1014 W/cm2. An experiment on the effect of increasing pressure with the flyer technique was also carried out, and showed that the shock pressure obtained with a flyer was six times more than that without a flyer.
Zonal flow excitation by Shukla–Varma modes in a nonuniform dusty magnetoplasma
Authors: Shukla P. K. , Stenflo L.
Published: September 2002

The nonlinear coupling between the Shukla–Varma (SV) modes and the zonal flows in a nonuniform dusty magnetoplasma is considered. By using a two-fluid model and the guiding center particle drifts, a pair of coupled mode equations is obtained. The latter are Fourier analyzed to obtain a nonlinear dispersion relation, which exhibits the excitation of zonal flows by the ponderomotive force of the SV modes. The increment of the parametrically excited zonal flows is presented. The relevance of our investigation to laboratory and space plasmas is discussed.
Optical properties of strain-balanced SiGe planar microcavities with Ge dots on Si substrates
Authors: Kawaguchi K. , Morooka M. , Konishi K. , Koh S. , Shiraki Y.
Published: September 2002

SiGe microcavities with Ge dots were fabricated by employing strain-balanced SiGe/Si Bragg reflectors, and it was observed that photoluminescence from Ge dots embedded in the microcavity structure was significantly modulated due to the cavity effect. The characteristic luminescence of the microcavity was observed up to 200 K, and the thermal activation energy of the luminescence was largely improved compared with that of cavities with quantum wells.
Turbidity measurements and amplitude scaling of critical solutions of polystyrene in methylcyclohexane
Authors: Zhou C.-S. , An X.-Q. , Xia K.-Q. , Yin X.-L. , Shen W.-G.
Published: September 2002

We report turbidity measurements for a series of solutions of polystyrene in methylcyclohexane with varying polymer molecular weights. The obtained correlation length ξ and the osmotic compressibility χ shows power law dependence on both the reduced temperature t (=|T−Tc|/Tc) and the molecular weights Mw of the polymers. We find that the relations ξ0(1−φc)0.85∝Mw0.18, and χ0(1−φc)−1.20∝Mw−0.09 proposed by An, Jiang, Chen, and Shen [Chem. Phys. Lett. 282, 403 (1998)] can be used to describe the present experimental results. Moreover, these relations appear to be better suited than a simple scaling for extracting the Mw-exponents. The exponents so obtained are found to be in excellent agreement with theoretical predictions.
Ion desorption induced by core-level excitation of H2O/Si(100): Evidence of desorption due to the multielectron excitation/decay
Authors: Tanaka S. , Mase K. , Nagaoka S. , Nagasono M. , Kamada M.
Published: September 2002

This work is an investigation of the desorption by O 1s excitation of ions from Si(100) reacted with water. Photoelectron, photostimulated desorption, and electron-ion coincidence spectroscopy are used to observe the process. When the incident photons have energy levels which are near the 1s threshold of O, they induce Auger decay that is accompanied by shakeup/off excitation and cascade Auger decay, and they are shown to be the main factor responsible for desorption in this case. When the photons have energy levels which are above the shakeup threshold, most of the desorption that occurs is a result of the shakeup excitation that accompanies the core excitation. In both cases, the desorption is induced by the respective multihole final states. The ion desorption yield for the two-hole final states of the normal process of Auger decay is small. The results are discussed, with the help of the Auger electron spectra, mainly in terms of the lifetime of the final state of Auger decay.
Hysteretic behavior in metallic granular matter
Authors: Dorbolo S. , Ausloos M. , Vandewalle N.
Published: September 2002

Various packings made of metallic grains have been electrically characterized. Electrical breakdown is observed in I–V curves. A well defined critical point separates the insulating and the conducting regime of the packing. The breakdown is reversible by submitting the packing to a small tap. This unusual property leads to hysteretic loops in I–V diagrams. The study of the behavior of I–V curves allows us to describe the system as a network of weak lossy contacts. The key parameter is the inner electrical field controlling the diode-like or diffusion-like state of the packing.
The effect of the diameter ratio on the absolute and convective instability of free coflowing jets
Authors: Sevilla A. , Gordillo J. M. , Martı́nez-Bazán C.
Published: September 2002

The stability of two coflowing streams with finite cross stream extent has been studied in both axisymmetric as well as plane geometries. Transition curves from convective to absolute instability have been obtained in terms of the control parameters, namely, the density ratio, S, the velocity ratio, Λ, and, more importantly, the diameter ratio, a. A new mode of instability caused by the external shear layer included in the velocity profile has been identified. It has also been found that this mode is responsible for triggering the absolute instability of configurations considered convectively unstable in the limit a→∞. Moreover, in the present study it has been shown that, when Λ=1, the critical density ratio necessary to sustain absolute instability in axisymmetric jets decreases with the diameter ratio as Sc∝a−4, while it decreases as Sc∝a−6/5 in plane jets. In more general situations, where Λ≠1, two modes of instability associated, respectively, with the inner and the outer shear layers coexist. The analysis reveals that the outer shear layer has a significant effect on the stability of the internal interface, especially for light jets, corresponding to S<1, when a is sufficiently close to unity. Furthermore, a new region of absolute instability has been described in the a–Λ–S parameter space.
Light scattering on phonons in quasi-one-dimensional antiferromagnet CsFeCl3⋅2H2O induced by magnetic ordering
Authors: Kurnosov V. S. , Peschanskii A. V. , Fomin V. I. , Yeremenko A. V. , Pashkevich Yu. G.
Published: September 2002

The appearance of new phonon lines in the Raman spectrum of the quasi-one-dimensional antiferromagnet CsFeCl3⋅2H2O as a consequence of magnetic ordering with a change of the unit cell volume was detected experimentally. An analysis of the possible mechanisms that might lead to the observed spectral features is done. A new mechanism of inducing Raman scattering on phonons from the boundary of the paramagnetic Brillouin zone is hypothesized.
Electronic structure and magneto-optical Kerr effect in the compound UCuP2
Authors: Horpynyuk O. , Nemoshkalenko V. V. , Antonov V. N. , Harmon B. N. , Yaresko A. N.
Published: September 2002

The optical and magneto-optical (MO) spectra of the fernary compound UCuP2 are investigated from first principles, using the fully relativistic Dirac linear-muffin-tin-orbital band structure method and density-functional theory in the local spin-density approximation. Within a band-like description of the 5f electrons, good agreement with the measured MO spectra is obtained. The origin of the Kerr rotation in the compound is examined.
Electronic excitations and correlations in quantum bars
Authors: Kuzmenko I. , Gredeskul S. , Kikoin K. , Avishai Y.
Published: September 2002

The spectrum of boson fields and two-point correlators are analyzed in a quantum bar system (a superlattice formed by two crossed interacting arrays of quantum wires), with a short-range interwire interaction. The standard bosonization procedure is shown to be valid, within the two-wave approximation. The system behaves as a sliding Luttinger liquid in the vicinity of the Γ point, but its spectral and correlation characteristics have either 1D or 2D nature depending on the direction of the wave vector in the rest of the Brillouin zone. Due to the interwire interaction, unperturbed states propagating along the two arrays of wires are always mixed, and the transverse components of the correlation functions do not vanish. This mixing is especially strong around the diagonals of the Brillouin zone, where the transverse correlators have the same order of magnitude as the longitudinal ones.
Influence of dissipation on a low-voltage dc current in a long SNS junction
Authors: Kulinich S. I. , Shekhter R. I.
Published: September 2002

The dc current through a voltage-biased long transparent SNS junction in a dissipative regime is considered. The problem under certain conditions is mapped onto exactly solvable model of energy pumping into a quasiballistic 1D quantum ring driven by time-dependent magnetic flux. A rich peak-like structure of the subgap current at low voltages is predicted. The maxima in the current correspond to resonant energy absorption for fractional values of the normalized bias voltage.
Assignment of the first five electronic states of Ar2+ from the rotational fine structure of pulsed-field-ionization zero-kinetic-energy photoelectron spectra
Authors: Rupper P. , Merkt F.
Published: September 2002

The I(1/2u), I(3/2g), I(1/2g), I(3/2u), and II(1/2u) states of Ar2+ have been investigated by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy following (1+1′) resonance-enhanced two-photon excitation via the 0u+ Rydberg state located below the Ar* ([3p]54s′[1/2]1)+Ar(1S0) dissociation limit of Ar2. By selecting single rotational levels of the intermediate state, the rotational structure of five of the six lowest electronic states of Ar2+ could be observed. Photoionization selection rules and the magnitude of the observed Ω-doubling of the rotational levels were used to derive unambiguous assignments of the electronic symmetry of the ionic states. From the analysis of the rotational structure, the equilibrium internuclear distances, the adiabatic ionization potentials, the dissociation energies and vibrational and anharmonic constants could be determined for the I(1/2u), I(3/2g), I(1/2g), I(3/2u), and II(1/2u) states of Ar2+. A map of the rotational energy level structure of these states, which includes complete symmetry labels, has been derived. The classification of the rotational structure of the first electronic states of Ar2+ in Hund’s cases (a), (b), and (c) is discussed on the basis of the dependence of the Σ2–2Π interaction on the internuclear separation.
A direct numerical simulation of K- and H-type flow transition in a heated vertical channel
Authors: Chen Yen-Cho , Chung J. N.
Published: September 2002

In this study, the transition of a low Reynolds number mixed convection flow in a vertical channel is investigated by direct numerical simulations. Both K-type and H-type disturbances are investigated. For the K-type transition, it is found that the kinetic energy generated by the thermal buoyant force is the main driving force and the rate of vorticity generation is largely enhanced in the very early transition stage. The most significant characteristics during this period are that the large and high-strength vortex structures develop rapidly, large-scale temperature fields are found in the central region of the channel, and the Nusselt number increases quickly. For the H-type transition, it shares most of the characteristics with those of the K-type flow. One important exception is that the vortex structures in the H-type flow are positioned in a staggered pattern instead of an ordered pattern found in the K-type flow. The streamwise period is double that in the K-type flow. For both types, the flow field bifurcates to a new quasisteady nonlinear state after the initial transient period. The flow structure of this bifurcated state consists of many medium-scale and weak vortices, which are distributed relatively uniformly in the entire flow domain. These vortex structures do not change significantly with time. The important characteristics of the new state are that the vortex structures are still relatively regular as time progresses and the shear production of kinetic energy reaches to a small but finite magnitude and it changes very slightly with time. For a typical case, the average Nusselt number of the new state is about 32% above that of the laminar flow and the temperature fluctuations are low-frequency and small-scale oscillations. Those characteristics agree well with the experimental observations.
Polymeric multimode waveguide based electro-optic modulator with a vertically configured dumping planar waveguide
Authors: Lu Xuejun , Jang Chiou-hung , An Dechang , Zhou Qingjun , Sun Lin , Zhang Xuping , Chen Ray T. , Dawson Dan
Published: September 2002

An electro-optic modulator based on a polymeric multimode waveguide coupler was developed. A guiding multimode waveguide with a vertically configured dumping planar waveguide was employed in the design to increase the device packing density. A modulation depth of 91% at 1330 nm was experimentally achieved. This device shows that the multimode optical waveguide with the vertically configured dumping planar waveguide is promising in electro-optic modulator designs. This modulator can be used in multimode optical interconnection systems such as data communications and fiber sensor networks.
Two-dimensional imaging of continuous-wave terahertz radiation using electro-optic detection
Authors: Nahata Ajay , Yardley James T. , Heinz Tony F.
Published: September 2002

We report the demonstration of two-dimensional electro-optic imaging using continuous-wave THz radiation. Two single-frequency laser diodes serve as the optical source for both the generation and detection processes. The generation process occurs by mixing in a photoconductive emitter, while the detection process utilizes an electro-optic crystal and charge coupled device camera. The method permits far-IR imaging using only conventional optical components held at room temperature. In this demonstration, we image the two-dimensional properties of a THz beam focused into a 〈110〉 ZnTe electro-optic detection crystal.
Growth front roughening of room-temperature deposited copper nanocluster films
Authors: Palasantzas G. , Koch S. A. , De Hosson J. Th. M.
Published: September 2002

Growth front aspects of copper nanocluster films deposited with low energy onto silicon substrates at room temperature are investigated by atomic force microscopy. Analyses of the height-difference correlation function yield a roughness exponent H of 0.45±0.05. The root-mean-sqaure roughness amplitude w evolves with deposition time as a power law, w∝tβ (β=0.62±0.07), leading also to a power-law increase of the local surface slope ρ, ρ∝tc (c=0.73±0.09). These scaling exponents, in combination with an asymmetrical height distribution, point at a complex nonlinear roughening mechanism dominated by the formation of voids resulting in a highly porous film.
The onset of absolute instability of rotating Hagen–Poiseuille flow: A spatial stability analysis
Authors: Fernandez-Feria R. , del Pino C.
Published: September 2002

A spatial, viscous stability analysis of Poiseuille pipe flow with superimposed solid body rotation is considered. For each value of the swirl parameter (inverse Rossby number) L>0, there exists a critical Reynolds number Rec(L) above which the flow first becomes convectively unstable to nonaxisymmetric disturbances with azimuthal wave number n=−1. This neutral stability curve confirms previous temporal stability analyses. From this spatial stability analysis, we propose here a relatively simple procedure to look for the onset of absolute instability that satisfies the so-called Briggs–Bers criterion. We find that, for perturbations with n=−1, the flow first becomes absolutely unstable above another critical Reynolds number Ret(L)>Rec(L), provided that L>0.38, with Ret→Rec as L→∞. Other values of the azimuthal wave number n are also considered. For Re>Ret(L), the disturbances grow both upstream and downstream of the source, and the spatial stability analysis becomes inappropriate. However, for Re<Ret, the spatial analysis provides a useful description on how convectively unstable perturbations become absolutely unstable in this kind of flow.
Aggregation and permeation of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran molecules in Alq
Authors: Zhong G. Y. , Xu Z. , He J. , Zhang S. T. , Zhan Y. Q. , Wang X. J. , Xiong Z. H. , Shi H. Z. , Ding X. M. , Huang W. , Hou X. Y.
Published: September 2002

The morphologic and luminescent behaviors of various 4-(dicyanomethylene)-2methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) containing films have been investigated. This involves pure DCM layers deposited on top of a tris-(8-hydroxyquinoline) aluminum (Alq) layer or positioned between two Alq layer, DCM-doped Alq films, and periodically arranged Alq/DCM multilayer structures. The occurrence over a period of time of aggregation and permeation of DCM molecules at room temperature and at temperatures as low as ∼260 K is found in all the cases studied. Such a phenomenon will result in degradation of related organic light-emitting devices and is closely related to the electric polarity of the DCM molecule.
Ferroelectric Pb(Zr,Ti)O3/Al2O3/4H–SiC diode structures
Authors: Koo S.-M. , Khartsev S. I. , Zetterling C.-M. , Grishin A. M. , Östling M.
Published: September 2002

Pb ( Zr,Ti ) O 3 (PZT) films (450 nm thick) were grown on 4H–silicon carbide (SiC) substrates by a pulsed-laser deposition technique. X-ray diffraction confirms single PZT phase without a preferred orientation. Stable capacitance–voltage (C–V) loops with low conductance (<0.1 mS/cm2, tan δ∼0.0007 at 400 kHz) and memory window as wide as 10 V were obtained when 5-nm-thick Al2O3 was used as a high band gap (Eg∼9 eV) barrier buffer layer between PZT (Eg∼3.5 eV) and SiC (Eg∼3.2 eV). High-frequency (400 kHz) C–V characteristics revealed clear accumulation, and depletion behavior. Although the charge injection from SiC is the dominant mechanism for C–V hysteresis in PZT/Al2O3/SiC, negligible sweep rate dependence and negligible applied bias dependence were observed compared to that of PZT/SiC. By using room-temperature photoilluminated C–V measurements, the interface states as well as the charge trapping in the PZT/Al2O3 stacks have been calculated.
Gain spectra of coupled InGaAsP/InP quantum wells measured with a segmented contact traveling wave device
Authors: Körbl M. , Gröning A. , Schweizer H. , Gentner J. L.
Published: September 2002

We use an adaptation of the variable stripe length method to measure the spectral gain of InGaAsP/InP laser structures with 12 coupled quantum films as active volume. The samples are prepared with a two-segment contact stripe for current injection, so the length of the electrically pumped region can be varied between two values. From the corresponding ratio of emission intensities, the gain spectra are extracted. Their analysis with respect to the dependency on the injected carrier density shows the possibility of a simple description of the gain of coupled quantum wells.
Methane conversion into acetylene in a microwave plasma: Optimization of the operating parameters
Authors: Heintze M. , Magureanu M.
Published: September 2002

The methane decomposition and the formation of C2 hydrocarbons, in particular acetylene, in a microwave plasma were studied. It was found that pulsing the discharge presents major advantages over the cw operation. The effect of the operating parameters, including pressure (15–65 mbar), flow rate (33–190 sccm), and discharge power (16–81 W) was investigated, with the aim to improve the efficiency for methane conversion and to reduce the energy requirement for the formation of acetylene. Maximum values of the methane conversion degree over 90% were obtained. As a function of the discharge conditions, acetylene can become the main reaction product, with 80% selectivity. The minimum energy requirement for methane conversion was approximately 7 eV/molecule and for acetylene formation 20 eV/molecule. The results show that active species generated in the plasma contribute to the methane dissociation and influence the product distribution. The correlation between the dehydrogenation and the gas temperature supports the view of thermally activated neutral–neutral reactions.
Real time probing of magnetization switching in magnetic nanostructures
Authors: Guittienne Ph. , Gravier L. , Wegrowe J.-E. , Ansermet J.-Ph.
Published: September 2002

Time-resolved anisotropic magnetoresistance (AMR) measurements of the irreversible switching of the magnetization were performed on isolated Ni nanowires. The magnetization reversal was triggered by injection of high current densities in a static magnetic field. The detection was achieved by means of a Wheatstone bridge with a 1 GHz bandwidth. Time-resolved switching was obtained in single shot measurements. Nanowires with diameter of about 100 nm that present a uniform rotation in the reversible regime detected in quasistatic AMR measurements are found to have switching in about 14 ns. This value can be accounted for in the framework of an uniform rotation model with value of the Gilbert damping coefficient of 0.005–0.01. Nanowires with larger diameters (typ. 200 nm) that manifest inhomogeneous magnetization in quasistatic AMR measurements have a switching time of about 37 ns.
Femtosecond laser induced crystallization and permanent relief grating structures in amorphous inorganic (In2O3+1 wt % TiO2) films
Authors: Katayama Shigeru , Tsutsumi Naoto , Nakamura Toshitaka , Horiike Mika , Hirao Kazuyuki
Published: September 2002

This letter presents an investigation of crystalline relief grating structures induced by irradiation of near-infrared femtosecond laser pulses on an amorphous inorganic (In2O3+1 wt % TiO2) film. The shapes of crystallized relief structures were sensitive to the scanning rate and the focused point height of irradiation, and the optimized irradiation condition gave cone-shaped cross section structures. Selective wet etching on unirradiated amorphous regions using a 3% hydrochloric acid solution could make sharper relief grating structures of crystalline regions. Diffraction efficiency of the relief grating structures with Au coating was measured, and it was confirmed that first-order diffraction, efficiencies were approximately 40% and 20% for etched and nonetched samples, respectively.
Neutral gas temperature estimate in CF4/O2/Ar inductively coupled plasmas
Authors: Cruden Brett A. , Rao M. V. V. S. , Sharma Surendra P. , Meyyappan M.
Published: September 2002

Neutral temperatures in inductively coupled CF4/O2/Ar mixture plasmas have been characterized by fitting the rotational envelope of emission spectra in a gaseous electronics conference reference cell. CF and CO are found to present different rotational temperatures with opposite trends with respect to pressure. It is proposed that CF is created as a rotationally and translationally hot molecule due to CF4 dissociation and the disparity in temperatures and temperature trend is indicative of incomplete equilibration of the CF with other neutral species in the plasma. This may have important consequences from the standpoint of understanding neutral reaction chemistries.
Large magnetocaloric effect in La(FexSi1−x)13 itinerant-electron metamagnetic compounds
Authors: Fujieda S. , Fujita A. , Fukamichi K.
Published: September 2002

The magnetocaloric effect (MCE) originated from the itinerant-electron metamagnetic transition for La(FexSi1−x)13 compounds has been investigated. With increasing Fe concentration, the MCE is enhanced and both the isothermal magnetic entropy change ΔSm and the adiabatic temperature change ΔTad for the compound with x=0.90 are −28 J/kg K and 8.1 K, respectively, by changing the magnetic field from 0 to 2 T. Similar large MCE values are achieved around room temperature by controlling the Curie temperature by means of hydrogen absorption. Consequently, La(FexSi1−x)13 compounds are promising as magnetic refrigerant materials working in relatively low magnetic fields.
Partial optimization of molecular geometry in normal coordinates and use as a tool for simulation of vibrational spectra
Authors: Bouř Petr , Keiderling Timothy A.
Published: September 2002

A normal mode coordinate-based molecular optimization algorithm was implemented and its performance tested against other optimization techniques. In certain cases the method was found to be computationally simpler and numerically more stable than the optimization algorithms based on Cartesian or internal valence coordinates. The usual redundant/internal coordinate scheme provided fastest convergence for compact covalently bonded molecules, while the normal mode method was found to be more suitable for more weakly bonded molecular complexes. For constrained optimizations use of the normal coordinates allows one to naturally separate the lower-energy modes from those more typically studied with vibrational spectroscopy. Thus, it provides an appropriate tool for simulations of IR and Raman spectra of larger molecules and complex systems when specific conformations are desired.
Dielectric properties and high tunability of Ba(Ti0.7Zr0.3)O3 ceramics under dc electric field
Authors: Yu Zhi , Ang Chen , Guo Ruyan , Bhalla A. S.
Published: September 2002

The effect of dc electric field (E) on the dielectric properties of Ba(Ti0.7Zr0.3)O3 ceramics with an obvious ferroelectric-relaxor behavior (Tm∼229 K, 10 kHz) is reported. The dielectric constant is greatly suppressed and a low loss is obtained under dc electric fields (⩽40 kV/cm). The low loss (tan δ∼0.002) and high tunability (∼45%) were obtained for the Ba(Ti0.7Zr0.3)O3 ceramics around 300 K, indicating that it is a promising candidate for tunable materials at room temperature. The field dependence of the temperature (Tm) of the dielectric constant maximum follows the ΔTm∼E2/3 relation, indicating a second-order phase-transition-like behavior.
Electrical transport through 60 base pairs of poly(dG)-poly(dC) DNA molecules
Authors: Hwang J. S. , Kong K. J. , Ahn D. , Lee G. S. , Ahn D. J. , Hwang S. W.
Published: September 2002

We report electrical transport through 60 base pairs of poly(dG)-poly(dC) DNA molecules. The DNA solution is dropped on two metal electrodes with the gap of 20 nm. The current–voltage characteristics measured between the electrodes exhibits clear staircases, which are reproducible over repeated measurements. The size of the observed staircases is consistent with the energy gap obtained from a tight binding calculation.
Electronic structure of nanometer-scale GaAs whiskers
Authors: Persson M. P. , Xu H. Q.
Published: September 2002

We report a theoretical study of the electronic structure of GaAs nanowhiskers, grown in the [111] direction with hexagonal cross section, based on a tight binding approach. It is shown that the band structure of the GaAs nanowhiskers shifts from a direct band gap to an indirect band gap when the lateral size of the nanowhiskers becomes smaller than a certain value. The effective masses of the electrons and holes are shown to increase with decreasing the nanowhisker lateral size. It is also shown that the light-hole states appear to be at the top of the valence bands. The electrical and optical properties of the nanowhiskers are discussed in terms of the results of the calculations.
Boron penetration studies from p+ polycrystalline Si through HfSixOy
Authors: Quevedo-Lopez M. A. , El-Bouanani M. , Kim M. J. , Gnade B. E. , Wallace R. M. , Visokay M. R. , LiFatou A. , Bevan M. J. , Colombo L.
Published: September 2002

We present detailed B penetration studies from B-doped polysilicon through alternate gate dielectric candidate HfSixOy films. No detectible B penetration is observed for annealing times as long as 20 s after 950 °C. Considerable B incorporation into the Si substrate is observed for annealing temperatures higher than 950 °C. By modeling the B depth profiles, we calculated the B diffusivities through HfSixOy to be higher than the corresponding diffusivities for SiO2. B diffusion through grain boundaries after HfSixOy crystallization is proposed to be responsible for the enhanced B diffusivity observed.
Displacement of a two-dimensional immiscible droplet in a channel
Authors: Kang Qinjun , Zhang Dongxiao , Chen Shiyi
Published: September 2002

We used the lattice Boltzmann method to study the displacement of a two-dimensional immiscible droplet subject to gravitational forces in a channel. The dynamic behavior of the droplet is shown, and the effects of the contact angle, Bond number (the ratio of gravitational to surface forces), droplet size, and density and viscosity ratios of the droplet to the displacing fluid are investigated. For the case of a contact angle less than or equal to 90°, at a very small Bond number, the wet length between the droplet and the wall decreases with time until a steady shape is reached. When the Bond number is large enough, the droplet first spreads and then shrinks along the wall before it reaches steady state. Whether the steady-state value of the wet length is greater or less than the static value depends on the Bond number. When the Bond number exceeds a critical value, a small portion of the droplet pinches off from the rest of the droplet for a contact angle less than 90°; a larger portion of the droplet is entrained into the bulk for a contact angle equal to 90°. For the nonwetting case, however, for any Bond number less than a critical value, the droplet shrinks along the wall from its static state until reaching the steady state. For any Bond number above the critical value, the droplet completely detaches from the wall. Either increasing the contact angle or viscosity ratio or decreasing the density ratio decreases the critical Bond number. Increasing the droplet size increases the critical Bond number while it decreases the critical capillary number.
6 W InGaAsSb(Gd)/InAsSbP double-heterostructure diode lasers emitting at λ=3.3 μm
Authors: Aydaraliev M. , Zotova N. V. , Karandashov S. A. , Matveev B. A. , Remennyi M. A. , Stus’ N. M. , Talalakin G. N. , Bewley W. W. , Lindle J. R. , Meyer J. R.
Published: September 2002

An InGaAsSb/InAsSbP double-heterostructure laser (λ=3.3 μm) with Gd-doped active region exhibited 6 W (35 A and 150 ns) of output power in pulsed mode at 78 K. The power, spectral, and electrical characteristics are presented, along with their temperature dependences.
Microscopic theories of model macromolecular fluids and fullerenes: The role of thermodynamic consistency
Authors: Caccamo Carlo , Pellicane Giuseppe
Published: September 2002

We investigate the accuracy of two well-known integral equation theories (IETs) of the fluid state, namely, the modified hypernetted chain (MHNC) approximation and the hybridized mean spherical approximation (HMSA), as applied to systems characterized by short-range interactions. The theoretical approaches are implemented by enforcing their thermodynamic consistency according to two different strategies: in one case the equality of the isothermal compressibility, as calculated via the virial and fluctuation routes from structure to thermodynamics, is imposed [“local” consistency (LC)]; in the other case the equality of the pressure as calculated either via the two previous routes, or via the virial and the energy routes, is imposed [“global” consistency (GC)]. We show that for the class of potentials at issue the GC is in general considerably more accurate than the LC. We document this result by investigating the performances of the MHNC and the HMSA, as applied to the calculation of the thermodynamic and structural properties of the hard-core Yukawa (HCY) potential, the Derjaguin–Landau–Vervey–Overbeek (DLVO) potential and the Girifalco potential for fullerenes. The obtained results are then compared with Monte Carlo simulation data, that we also produce for the same model systems. As far as the HCY potential is concerned, the investigation covers a range of the Yukawa inverse decay length, z, spanning from z=1.8 when the interaction mimics the Lennard-Jones 12-6 potential, to z=7 when the potential mimics the “effective” short range interaction between globular proteins in a highly charge-screened aqueous solution. IETs are then applied to the DLVO potential with charge and Hamaker constant values which fit the dynamical interaction factor of lysozyme in a solution of high ionic strength, and to the Girifalco potential with parameters appropriate to model C60 and C70. It emerges from the present study that the GC is able to provide Helmholtz free energies and chemical potentials which compare quite favorably with the simulation data. As a consequence, we are able to show that the GC estimates of the phase coexistence densities for the HCY and Girifalco potential agree almost quantitatively with the Monte Carlo ones, by thus definitely improving upon previous results obtained within the LC. We also comment on the relevance of confident phase diagram determinations from IETs, in connection with the prediction of protein crystallization. Possible extensions of the present thermodynamic consistency strategies to more sophisticated theories and realistic models of protein solutions and fullerenes are finally suggested.
Molar volumes of molten indium at high pressures measured in a diamond anvil cell
Authors: Shen Guoyin , Sata Nagayoshi , Newville Mathew , Rivers Mark L. , Sutton Stephen R.
Published: September 2002

Molar volumes of molten indium have been measured in an isothermal compression up to 8.5 GPa at 710(3) K in an externally heated diamond anvil cell. The measurement is based on the x-ray diffraction and x-ray absorption of materials using a synchrotron monochromatic x-ray microbeam. The fit to the results with the Birch–Murnaghan equation of state gives parameters of V0=16.80 cm3, K0=23.9(6) GPa, assuming that K′=4. This method should be applicable for measuring molar volumes of liquids and other amorphous materials in the diamond anvil cell.
Millimeter-wave dielectric properties of electro-optic polymer materials
Authors: Lee Mark , Mitrofanov O. , Katz H. E. , Erben C.
Published: September 2002

The complex dielectric constant of several polymer matrix materials and chromophore molecules of potential use in very high-speed electro-optic (EO) devices have been measured from 10 to 400 GHz. For all matrices, the index of refraction n is relatively low (1.3<n<2.0) and has little dispersion up to at least 250 GHz. Upon including an EO chromophore into the host, n increases up to 15%. The dielectric loss tangent is small (∼10−4) in most cases. Use of these properties to velocity match a guided millimeter wave mode with a guided optical mode will be discussed.