bluuebunny/crossref_metadata_2025 huggingface dataset:
ac conductivity analysis for a metal core-silver orthosilicate shell nanostructure
Authors: Ghosh B. , Chakravorty D. , Macdonald J. R. , Das G. C.
Published: April 2006

Nanocomposites containing silver particles of diameter of 20nm with silver orthosilicate crystals forming the shell with thickness around 21nm closely packed in a silicate glass were prepared. The ac conductivity of samples subjected to different heat treatments were measured over the frequency range of 100Hzto6MHz in the temperature range of 500–570K. The data were analyzed by the Macdonald model based on Kohlrausch-related frequency response formalism designated as CK0. The reference system was taken as the glass-crystal composite containing a lithium orthosilicate crystalline phase. The shape parameter βo for the reference system was found to be 0.33, whereas that for the nanocomposites was extracted to be 0.46. The former implied a one-dimensional lithium ion motion along the grain boundaries of the orthosilicate crystals, whereas the latter indicated that there was a one-dimensional silver ion motion in an effective two-dimensional structure in the shell surface because of a high stress condition along the radial direction of the core-shell composite.
On the origin of the Staebler-Wronski effect
Authors: Krüger Thomas
Published: April 2006

The parametrization of our recently proposed model of the Staebler-Wronski effect (SWE) is improved, which leads to an even better agreement with the experimental photoconductivity of light-soaked a-Si:H. The numerical solution of the essential equation exhibits well the typical SWE behavior, and it will be shown that previously raised arguments against our model are unfounded.
Electric-field-induced disclination migration in a Grandjean-Cano wedge
Authors: Strömer J. F. , Marenduzzo D. , Brown C. V. , Yeomans J. M. , Raynes E. P.
Published: April 2006

The behavior of a disclination line in a Grandjean-Cano wedge is investigated under an electric field applied normal to the cell substrates. The focus of attention is the first disclination, separating the untwisted and the π-twisted area. This disclination line shows a field dependent migration process that was observed in the cholesteric mixture ZLI-1132/S811. The dynamics of this migration process is studied experimentally and is compared with two theoretical models. One model utilizes a two-dimensional lattice Boltzmann approach to predict the initial migration movement, whereas a one-dimensional continuum model allows a full analysis of the experimental results.
Convective flows in a two-layer system with a temperature gradient along the interface
Authors: Nepomnyashchy Alexander A. , Simanovskii Ilya B.
Published: April 2006

The nonlinear stability of two superposed horizontal liquid layers bounded by two solid planes and subjected to a horizontal temperature gradient, is investigated. Two types of boundary conditions, periodic boundary conditions and heat-insulated lateral walls, are considered. The nonlinear simulations of the wavy convective regimes for a particular set of fluids, are performed. The dependence of the direction of the wave propagation depends on two factors, which are studied, the ratio of the layers thicknesses and the Marangoni number.
Isotope quantum effects in water around the freezing point
Authors: Hart R. T. , Mei Q. , Benmore C. J. , Neuefeind J. C. , Turner J. F. C. , Dolgos M. , Tomberli B. , Egelstaff P. A.
Published: April 2006

We have measured the difference in electronic structure factors between liquid H2O and D2O at temperatures of 268 and 273K with high energy x-ray diffraction. These are compared to our previously published data measured from 279to318K. We find that the total structural isotope effect increases by a factor of 3.5 over the entire range, as the temperature is decreased. Structural isochoric temperature differential and isothermal density differential functions have been used to compare these data to a thermodynamic model based upon a simple offset in the state function. The model works well in describing the magnitude of the structural differences above ∼310K, but fails at lower temperatures. The experimental results are discussed in light of several quantum molecular dynamics simulations and are in good qualitative agreement with recent temperature dependent, rotationally quantized rigid molecule simulations.
Vibrational and rotational energy transfers involving the CH B Σ−2 v=1 vibrational level in collisions with Ar, CO, and N2O
Authors: Huang Hong-Yi , Tsai Ming-Tsang , Lin King-Chuen
Published: April 2006

With photolysis-probe technique, we have studied vibrational and rotational energy transfers of CH involving the B Σ−2 (v=1, 0⩽N⩽6, F) state by collisions with Ar, CO, and N2O. For the vibrational energy transfer (VET) measurements, the time-resolved fluorescence of the B-X(0,0) band is monitored following the (1,0) band excitation. For the rotational energy transfer (RET) measurements, the laser-induced fluorescence of the initially populated state is dispersed using a step-scan Fourier transform spectrometer. The time-resolved spectra obtained in the nanosecond regime may yield the RET information under a single pressure of the collider. The rate constants of intramolecular energy transfers are evaluated with simulation of kinetic models. The VET lies in the range of 4×10−12to4×10−11cm3molecule−1s−1, with efficiency following the order of Ar<CO<N2O, reflecting the average over Boltzmann rotational distribution. The RET rates are more rapid by one to two orders of magnitude, comparable to the gas kinetic, with the trend of Ar<CO<N2O. The transfer rates decrease with increasing N and ΔN, proceeding via the ΔN=−1 transitions slightly larger than ΔN=+1. With the fine-structure labels resolved up to N=6, the fine-structure-conserving collisions prevail increasingly with increasing N in ΔN≠0. The rate constants for the F2→F1 transitions are larger than the reverse F1→F2 transitions in ΔN=0 for the Ar and CO collisions. The trend of fine-structure conservation is along the order of N2O<CO∼Ar. For the CH–Ar collisions, the fine-structure conservation is less pronounced as compared with the v=0 level reported previously. In general, the propensity rules obeyed in the v=0 collision with Ar are valid in v=1, but the latter case shows a weaker tendency. It might be caused by the anisotropy difference of interaction potential when vibrational excitation is considered. For the polyatomic collider, the strong long-range dipole-dipole interaction may have the chance to vary the rotational orientation to increase the fine-structure-changing transitions.
Thermal convection in superposed fluid and porous layers subjected to a plane Poiseuille flow
Authors: Chang Min-Hsing
Published: April 2006

Thermal convection in a two-layer system comprised by a fluid layer overlying a layer of porous media saturated with the same fluid has been investigated. The system is heated from below and subjected to a horizontally plane Poiseuille flow. The interaction between both instability mechanisms, the unstably stratification and the shear arising from the plane Poiseuille flow, is studied and a completely linear stability analysis has been carried out by considering both longitudinal rolls (LRs) and transverse rolls (TRs). It is found that the neutral curves of both modes may be bimodal, which is dependent on the depth ratio, the ratio of the depth of fluid layer to that of the porous layer. The stability characteristics of LRs are found to be invariant with the Reynolds number based on the horizontal Poiseuille velocity and the Prandtl number of the fluid, and the instability is always dominated by this mode if the Reynolds number is within low or moderate strength. The superimposed Poiseuille flow seems to exert a stabilizing effect on the traveling TRs and the critical transverse mode tends to be within the porous layer with low propagating speed. However, if the Reynolds number is sufficiently large, a shear instability mode appears abruptly with higher propagating speed and then dominates the system instability.
Nucleation of pentacene thin films on silicon dioxide modified with hexamethyldisilazane
Authors: Killampalli Aravind S. , Engstrom J. R.
Published: April 2006

Nucleation and growth of pentacene on silicon dioxide surfaces modified with hexamethyldisilazane, HN[Si(CH3)3]2, has been examined using supersonic molecular beam techniques and atomic force microscopy. Similar to growth on clean SiO2 surfaces, the rate of deposition at a fixed incident flux decreases with increasing kinetic energy of incident pentacene, indicative of trapping mediated adsorption. Unlike clean, unmodified SiO2 surfaces, however, growth on the modified surface exhibits characteristics of heterogeneous nucleation, where the maximum island density is independent of deposition rate. Further, islands in the submonolayer regime are two molecules high, unlike the one molecule high islands observed on clean SiO2.
Structure and dielectric relaxation properties of Na1−xLaxNb1−xCrxO3 perovskites
Authors: Hsiao Yu-Jen , Chang Yen-Hwei , Fang Te-Hua , Chang Yee-Shin , Chai Yin-Lai
Published: April 2006

Na 1 − x La x Nb 1 − x Cr x O 3 perovskites were prepared by conventional solid-state reaction with x=0.01, 0.05, 0.1, 0.2, 0.3, and 0.4. The structure with x=0.01 is similar to that of NaNbO3 with an orthorhombic structure. The crystal structure for compositions for x over 0.05 was found to have a distorted cubic structure. Grains of microcube topography were obtained. The average grain size is about 1–2μm. The dielectric constants and dissipation factors were measured as functions of frequency (20Hz–1MHz) and temperature (225–500K). The activation energy for x=0.2, 0.3, and 0.4 were 0.22, 0.21, and 0.19eV, respectively. Space charge polarization and orientational polarization contribute to the observed dielectric behavior.
Quantum simulation of resonant tunneling in nanoscale tunnel transistors
Authors: Shin Mincheol , Jang Moongyu , Lee Seongjae
Published: April 2006

We have performed ballistic and diffusive quantum simulations of resonant tunneling in nanoscale tunnel transistors. We have investigated three factors, temperature, interference, and diffusive scattering, which may affect the resonant tunneling effect in the devices. Our simulations indicate that if the channel length and depth are in the order of tens of nanometers and a few nanometers, respectively, and the electron mean free path in the channel region is in the order of tens of nanometers, the current oscillations and the negative differential resistance behavior due to resonant tunneling may be observed at room temperature.
Probing residual strain in InGaAs∕GaAs micro-origami tubes by micro-Raman spectroscopy
Authors: Bernardi A. , Goñi A. R. , Alonso M. I. , Alsina F. , Scheel H. , Vaccaro P. O. , Saito N.
Published: April 2006

We have experimentally investigated nanostructures consisting of free-standing microtubes with diameters in the micrometer range fabricated by rolling-up InGaAs∕GaAs bilayers grown by molecular-beam epitaxy on a GaAs substrate. The formation of the microtubes is powered by the built-in strain in the InGaAs layer and they develop after releasing the bilayer structure from the substrate by selective etching. Through micro-Raman spectroscopy we were able to detect the residual strain of the microtube, which results in a frequency shift of phonon modes measured on the tube as compared with reference unstrained material. We developed a simple elastic model to describe the measured phonon frequency shifts, from which we estimate the strain status of the microtube. Results demonstrate the power of Raman spectroscopy as a diagnostic tool for engineering of strain-driven self-positioning microelectromechanical systems.
Fabrication of superconducting MgB2 nanostructures by an electron beam lithography-based technique
Authors: Portesi C. , Borini S. , Amato G. , Monticone E.
Published: April 2006

In this work, we present the results obtained in fabrication and characterization of magnesium diboride nanowires realized by an electron beam lithography (EBL)-based method. For fabricating MgB2 thin films, an all in situ technique has been used, based on the coevaporation of B and Mg by means of an e-gun and a resistive heater, respectively. Since the high temperatures required for the fabrication of good quality MgB2 thin films do not allow the nanostructuring approach based on the lift-off technique, we structured the samples combining EBL, optical lithography, and Ar milling. In this way, reproducible nanowires 1μm long have been obtained. To illustrate the impact of the MgB2 film processing on its superconducting properties, we measured the temperature dependence of the resistance on a nanowire and compared it to the original magnesium diboride film. The electrical properties of the films are not degraded as a consequence of the nanostructuring process, so that superconducting nanodevices may be obtained by this method.
Micropropulsion devices based on molecular acceleration by pulsed optical lattices
Authors: Shneider Mikhail N. , Gimelshein Sergey F. , Barker Peter F.
Published: April 2006

The ability of a traveling periodic optical potential to increase the thrust and specific impulse of microthrusters is investigated. Two flow regimes, high density and low density, are considered. The thrust from a micronozzle, with a stagnation pressure of 1atm and temperature of 300K, can be increased by more than an order of magnitude. These conditions can be achieved for a constant velocity lattice, produced by two near counterpropagating optical fields that are focused into the nozzle throat. A propulsion system that operates in low-density regime and is driven by molecules trapped by an accelerating optical lattice is proposed. It is shown that such a system has a potential to achieve a specific impulse of thousands of seconds.
Point vortex motion on the surface of a sphere with impenetrable boundaries
Authors: Crowdy Darren
Published: April 2006

A conformal mapping approach to the problem of the motion of a single point vortex in a simply connected region bounded by impenetrable walls on the surface of a sphere is presented. Several illustrative examples are given, including those considered by previous authors using arguments based on the method of images. A new example of the motion of a vortex around a straight barrier along a great circle on the spherical surface is studied in detail. Finally, a theoretical connection with a boundary value problem for a generalized Liouville-type quasilinear partial differential equation is also made.
Direct numerical simulation of turbulent channel flows with boundary roughened with virtual sandpaper
Authors: Scotti Alberto
Published: April 2006

A method to simulate the effects of a roughened surface on a turbulent boundary layer is introduced. The method is easy to implement, does not increase the numerical overhead of the code, and affects the mean velocity in an a priori predictable way. A single parameter k is sufficient to fully characterize the roughness. The procedure has been tested in turbulent channel flows at Reτ=1000, with roughness heights k+ spanning the transitional regime. The properties of the rough flow agree well with experimental data.
Impact of absorption mechanisms on Kerr-nonlinear resonator behavior
Authors: Priem Gino , Bienstman Peter , Morthier Geert , Baets Roel
Published: April 2006

The effect of both single-photon and two-photon absorption mechanisms on the Kerr-nonlinear behavior of resonant structures is investigated using a semianalytical, one-dimensional model. In particular, two-photon effects may severely degrade the ultrafast, nonlinear potential of these structures. Based on this model, the feasibility of Kerr-nonlinear operation is derived for the AlGaAs and Si material systems.
Co
∕
Pt
multilayers with large coercivity and small grains
Authors: Shan R. , Gao T. R. , Zhou S. M. , Wu X. S. , Fang Yi-Kun , Han Bao-Shan
Published: April 2006

Multilayers of [Co∕Pt]20, with tCo∕tPt≐7 and the period Λ in the range of 0.27–0.69nm, and [Co(0.46nm)∕Pt(0.07–0.14nm)]20 have been prepared by sputtering at low deposition rates and a high Ar pressure of 7.8Pa. Structure and magnetic properties were characterized by x-ray diffraction, transmission electron microscopy, magnetometry measurements, and magnetic force microscopy. Column structure, coherent stacking of Co and Pt layers, and small grains have been observed. The average atomic interplane distance d111 changes with the constituent layer thickness. In the first series of Co∕Pt multilayers, the out-of-plane coercivity gradually increases to reach a maximum, with the bilayer period increasing from 0to0.58nm, and decreases with further increasing period. For the second series, the out-of-plane coercivity increases to reach a maximum of 6.5kOe with tPt increasing from 0.07to0.13nm and decreases with further increasing tPt. In order to explain the strong magnetic perpendicular anisotropy, the magnetoelastic energy of CoPt alloy layers must be taken into account.
Calibration of an isotopically enriched carbon-13 layer pressure sensor to 156GPa in a diamond anvil cell
Authors: Qiu Wei , Baker Paul A. , Velisavljevic Nenad , Vohra Yogesh K. , Weir Samuel T.
Published: April 2006

An isotopically enriched C13 homoepitaxial diamond layer of 6±1μm thickness was grown on top of a brilliant cut diamond anvil by a microwave plasma chemical vapor deposition process for application as a pressure sensor. This isotopically enriched diamond tip was then used in conjunction with a natural isotopic abundance diamond anvil to generate high pressure on the sample. We provide a calibration for the C13 Raman mode of this extremely thin epitaxial layer to 156GPa using ruby fluorescence and the equation of state of copper as secondary pressure standards. The nonlinear calibration of the C13 Raman mode pressure sensor is compared with similar calibrations of C12 Raman edge and a good agreement is obtained. The Raman signal from the C13 epitaxial layer remained a distinct singlet to 156GPa, and pressure calibration is independent of sample mechanical strength or the diamond anvil geometry. The use of even thinner layer would allow calibration further into ultrahigh pressure regime where the use of other optical sensors has proven to be difficult.
The Wigner-Weyl transformation and the quantum path integral
Authors: Bergeron H.
Published: April 2006

We show that the space of quantum states for a spinless particle possesses a (trivial) fiber bundle structure B×F where B is the classical phase space. This geometric point of view allows us to define a “quantum path integral” that connects quantum observables with their classical counterparts. We show that this path integral reduces in fact to the Wigner-Weyl transformation.
Reduced Gutzwiller formula with symmetry: Case of a finite group
Authors: Cassanas Roch
Published: April 2006

We consider a classical Hamiltonian H on R2d, invariant by a finite group of symmetry G, whose Weyl quantization Ĥ is a self-adjoint operator on L2(Rd). If χ is an irreducible character of G, we investigate the spectrum of its restriction Ĥχ to the symmetry subspace Lχ2(Rd) of L2(Rd) coming from the decomposition of Peter-Weyl. We give reduced semiclassical asymptotics of a regularized spectral density describing the spectrum of Ĥχ near a noncritical energy E∊R. If ΣE≔{H=E} is compact, assuming that periodic orbits are nondegenerate in ΣE∕G, we get a reduced Gutzwiller trace formula which makes periodic orbits of the reduced space ΣE∕G appear. The method is based upon the use of coherent states, whose propagation was given in the work of Combescure and Robert.
Thickness dependence of structural and piezoelectric properties of epitaxial Pb(Zr0.52Ti0.48)O3 films on Si and SrTiO3 substrates
Authors: Kim D. M. , Eom C. B. , Nagarajan V. , Ouyang J. , Ramesh R. , Vaithyanathan V. , Schlom D. G.
Published: April 2006

We report the structural and longitudinal piezoelectric responses (d33) of epitaxial Pb(Zr0.52Ti0.48)O3 (PZT) films on (001) SrTiO3 and Si substrates in the thickness range of 40nm–4μm. With increasing film thickness the tetragonality of PZT was reduced. The increase in d33 value with increasing film thicknesses was attributed to the reduction of substrate constraints and softening of PZT due to reduced tetragonality. The d33 values of PZT films on Si substrates (∼330pm∕V) are higher than those on SrTiO3 substrates (∼200pm∕V). The epitaxial PZT films on silicon will lead to the fabrication of high performance piezoelectric microelectromechanical devices.
Molecular dynamics investigations of the dissociation of SiO2 on an ab initio potential energy surface obtained using neural network methods
Authors: Agrawal Paras M. , Raff Lionel M. , Hagan Martin T. , Komanduri Ranga
Published: April 2006

The neural network (NN) procedure to interpolate ab initio data for the purpose of molecular dynamics (MD) simulations has been tested on the SiO2 system. Unlike other similar NN studies, here, we studied the dissociation of SiO2 without the initial use of any empirical potential. During the dissociation of SiO2 into Si+O or Si+O2, the spin multiplicity of the system changes from singlet to triplet in the first reaction and from singlet to pentet in the second. This paper employs four potential surfaces. The first is a NN fit [NN(STP)] to a database comprising the lowest of the singlet, triplet, and pentet energies obtained from density functional calculations in 6673 nuclear configurations. The other three potential surfaces are obtained from NN fits to the singlet, triplet, and pentet-state energies. The dissociation dynamics on the singlet-state and NN(STP) surfaces are reported. The results obtained using the singlet surface correspond to those expected if the reaction were to occur adiabatically. The dynamics on the NN(STP) surface represent those expected if the reaction follows a minimum-energy pathway. This study on a small system demonstrates the application of NNs for MD studies using ab initio data when the spin multiplicity of the system changes during the dissociation process.
Richtmyer-Meshkov instability induced by shock-bubble interaction: Numerical and analytical studies with experimental validation
Authors: Giordano J. , Burtschell Y.
Published: April 2006

This paper deals with the numerical study of the interaction of a shock wave and a bubble. The three different density ratio cases between air and bubble are investigated: light/heavy, heavy/light and close density. The numerical simulations are compared to the experiments of Layes et al. [Phys. Rev. Lett.91, 174502 (2003)]. These three cases may allow us to better understand the vortex deposition by the baroclinic terms. Moreover, the behavior differences between the deformation of a bubble and a cylinder collided by a shock wave are shown. An analytical approach to evaluate the final volume of an inhomogeneity submitted to a shock wave interaction is also presented and discussed.
Statistically steady measurements of Rayleigh-Taylor mixing in a gas channel
Authors: Banerjee Arindam , Andrews Malcolm J.
Published: April 2006

A novel gas channel experiment is described to study the development of high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air and the other containing a helium-air mixture, flow parallel to each other separated by a thin splitter plate. The streams meet at the end of a splitter plate leading to the formation of an unstable interface and of buoyancy driven mixing. This buoyancy driven mixing experiment allows for long data collection times, has short transients, and is statistically steady. The facility was designed to be capable of large Atwood number studies (At∼0.75). We describe initial validation work to measure the self similar evolution of mixing at density differences (0.035<At<0.1). The purpose of this paper is to describe the new high Atwood number gas channel facility and present validation results for experimental runs at Atwood numbers up to 0.1. Diagnostics include a constant temperature hot wire anemometer, and high resolution digital image analysis. The hot-wire probe gives velocity statistics of the mixing layer. A multiposition single-wire technique was used to measure the velocity fluctuations in three mutually perpendicular directions. Analysis of the measured data was used to explain the mixing as it develops to a self-similar regime in this flow. A digital image analysis procedure was used to characterize various properties of the flow and also to validate the hot wire measurements.
“Force-free” electrophoresis?
Authors: Yariv Ehud
Published: April 2006

When a colloidal particle is exposed to an externally applied electric field, it acquires an electrophoretic velocity, resulting from fluid slip occurring across the Debye screening layer. When the field is uniformly applied, it is usually assumed that the net neutrality of the combined particle-layer system implies that the net electric force acting on it must vanish. This assumption of “force-free” phoretic motion has been employed extensively to describe electrophoresis in both unbounded and bounded fluid domains [J. L. Anderson, Annu. Rev. Fluid Mech. 21, 61 (1989)]. A careful inspection reveals here that this intuitive premise may fail when the fluid domain is bounded, in which case a nonzero electric force (resembling dielectrophoretic forces in nonuniformly applied fields) may actually exist. Such forces (represented via surface integrals of Maxwell stresses) result in particle motion above and beyond the one driven by the phoretic slip mechanism. A positive demonstration for the existence of a such a force is provided for a standard sphere-wall configuration, where the applied field acts parallel to the wall. In that scenario, particle motion consists of a (familiar) slip-driven contribution parallel to the wall, together with a superimposed force-driven drift away from the wall. An analogy with pressure forces occurring at incompressible and inviscid potential flows is presented.
Turbulent structure beneath air-water interface during natural convection
Authors: Bukhari Syed J. K. , Siddiqui M. H. Kamran
Published: April 2006

Results from an experimental study investigating the turbulent structure beneath the air-water interface during natural convection are reported. The two-dimensional velocity field beneath the surface in a plane perpendicular to the surface was measured using digital particle image velocimetry. The results show that the waterside flow field undergoes three-dimensional flow interactions forming complex flow patterns, which appear to be random. The magnitude of the turbulent velocities and turbulent kinetic energy increases with the heat flux. The profiles of the turbulent velocities are self-similar and appropriately scaled by the parameters proposed for the natural convection above a heated wall. The wave number and frequency spectra exhibit −3 slopes providing the evidence that during natural convection the buoyancy subrange exists within the inertial subrange where the energy loss is due to the work against buoyancy.
Physical and electrical properties of nanolaminated HfO2∕LaAlO3∕HfO2 dielectric on Si
Authors: Liang Y. , Theodore N. D. , Curless J. , Tracy C.
Published: April 2006

Because of high defectivity and poor uniformity in polycrystalline HfO2, searching for an amorphous dielectric with a high dielectric constant and good stability has become an increasingly important task for high-k gate-stack research. We show that nanolaminated HfO2∕LaAlO3∕HfO2 dielectric grown on Si not only remains amorphous after annealing in N2 at 900°C for 60s but also has an effective dielectric constant comparable to that of HfO2. Additionally, electrical characterization of the capacitors made from the laminated dielectric revealed a smaller hysteresis and improved voltage stress behavior compared to its polycrystalline HfO2 counterpart.
Novel variable separation solutions and exotic localized excitations via the ETM in nonlinear soliton systems
Authors: Dai Chao-qing , Zhang Jie-fang
Published: April 2006

In this paper, first, the ETM is applied to obtain variable separation solutions of (2+1)-dimensional systems. A common formula with some arbitrary functions is derived to describe suitable physical quantities for some (2+1)-dimensional models such as the generalized Nizhnik-Novikov-Veselov, Davey-Stewartson, Broer-Kaup-Kupershmidt, Boiti-Leon-Pempinelli, integrable Kortweg-de Vries (KdV), breaking soliton and Burgers models. The universal formula in Tang, Lou, and Zhang [Phys. Rev. E 66, 046601 (2002)] can be simplified to the common formula in the present paper, which indicates that redundant process is included there since the easier variable separation form can be employed without loss of generality. Second, this method is successfully generalized to (1+1)-dimensional systems, such as coupled integrable dispersionless, long-wave–short-wave resonance interaction and negative KdV models, and obtain another common formula to describe suitable physical fields or potentials of these (1+1)-dimensional models, which is similar to the one in (2+1)-dimensional systems. Moreover, it also is extended to (3+1)-dimensional Burgers system, and find that the common formula in (2+1)-dimensional systems is also appropriate to describe the (3+1)-dimensional Burgers system. The only differences are that the function q is a solution of a constraint equation and p is an arbitrary function of three independent variables. Finally, based on the common formula for (2+1)-dimensional systems and by selecting appropriate multivalued functions, interactions among special dromion, special peakon and foldon are investigated. The interactions between two special dromions, and between two special peakons, both possess novel properties, that is, there exist a multivalued foldon in the process of their collision, which is different from the reported cases in previous literature. Furthermore, the explicit phase shifts for all the local excitations offered by the common formula have been given, and are applied to these novel interactions in detail.
Partial molar volume of n-alcohols at infinite dilution in water calculated by means of scaled particle theory
Authors: Graziano Giuseppe
Published: April 2006

The partial molar volume of n-alcohols at infinite dilution in water is smaller than the molar voulme in the neat liquid phase. It is shown that the formula for the partial molar volume at infinite dilution obtained from the scaled particle theory equation of state for binary hard sphere mixtures is able to reproduce in a satisfactory manner the experimental data over a large temperature range. This finding implies that the packing effects play the fundamental role in determining the partial molar volume at infinite dilution in water also for solutes, such as n-alcohols, forming H bonds with water molecules. Since the packing effects in water are largely related to the small size of its molecules, the latter feature is the ultimate cause of the decrease in partial molar volume associated with the hydrophobic effect.
Optical property and Stokes’ shift of Zn1−xCdxO thin films depending on Cd content
Authors: Kang Hong Seong , Kim Jae Won , Kim Jong Hoon , Lee Sang Yeol , Li Y. , Lee Jang-Sik , Lee J. K. , Nastasi M. A. , Crooker S. A. , Jia Q. X.
Published: April 2006

Ternary Zn1−xCdxO films were grown on (0001) sapphire substrates by pulsed laser deposition. The energy band gap of Zn1−xCdxO films decreases with increasing Cd content. An increase of Cd content also leads to the emission broadening, absorption edge broadening, and crystallinity degradation. The absorption edge and ultraviolet emission energy shift to lower energy from 3.357eVto3.295eV and 3.338eVto3.157eV, respectively, with increasing Cd content from 0.3% to 3% at 4K. The Stokes’ shift between the absorption and emission is observed and that indicates the increase of exciton localization with Cd content.
Lateral shifts of optical beams on the interface of anisotropic metamaterial
Authors: Cheng Qiang , Cui Tie Jun
Published: April 2006

We investigate the lateral shift of the optical beams incident from an ordinary isotropic medium into an anisotropic metamaterial half space. Different from the isotropic case, the shift is closely related to the dispersion relation of the anisotropic medium and some anomalous phenomena have been discovered. The lossy effect of the metamaterial on the lateral shift is also investigated, showing that the shift may be either negative or positive with respect to the incident angle. Analytical and numerical results validate the above conclusions.
Temperature dependent refractive index of amorphous silicon determined by time-resolved reflectivity during low fluence excimer laser heating
Authors: Hoyland J. D. , Sands D.
Published: April 2006

The temperature dependent refractive index of amorphous silicon has been measured at a wavelength of 820nm from room temperature up to nearly the melting point close to 1200°C. The method employed is to use a single pulse from a XeCl excimer laser to heat the silicon without crystallizing it and to measure the transient reflectivity. This is then modeled by converting a calculated temperature profile into an effective multilayer structure and calculating the reflectivity using a transfer matrix formulation. The refractive index is optimized using simulated annealing. The real part of the refractive index is found to vary linearly with a temperature coefficient of 3.85×10−4 while the extinction coefficient is found to vary as exp(3.82×10−3T), with T=0 at room temperature.
Ferromagnetic resonance studies in granular Co–SiO2 thin films
Authors: Pires M. J. M. , Denardin J. C. , da Silva E. C. , Knobel M.
Published: April 2006

Properties of thin granular Co–SiO2 films have been studied by means of ferromagnetic resonance (FMR). The obtained FMR results are discussed using sample magnetization, electrical conductivity, and transmission electron microscopy analysis. Co and SiO2 were sequentially deposited for the sample preparation. The general behavior of the applied field for resonance could be described using effective out-of-plane anisotropies. A dipolar interaction model developed for magnetic heterostructures was applied to the interpretation of these anisotropies. The anisotropy terms caused by the magnetic particle shapes and by the film shape can explain the results for two metallic films close to percolation, in which the film shape is the preponderant contribution. In the case of an insulating sample, the consideration of an additional anisotropy term seems to be necessary to explain the results.
Analytical and numerical calculations of the dispersion characteristics of two-dimensional dielectric photonic band gap structures
Authors: Samokhvalova Ksenia , Chen Chiping , Qian Bao-Liang
Published: April 2006

An exact analytical dispersion relation is derived for transverse-magnetic modes with kz=0 in a particular two-dimensional rectangular photonic band gap structure. The dispersion relation is analyzed, and the dispersion characteristics are determined. Analytical results are compared with results from the Massachusetts Institute of Technology Photonic Band Gap Structure Simulator (PBGSS) code. The error tolerance in the PBGSS code is established. Finally, the attenuations of modes with frequencies in global band gaps are computed analytically.
Nonmodal energy growth and optimal perturbations in compressible plane Couette flow
Authors: Malik M. , Alam Meheboob , Dey J.
Published: April 2006

Nonmodal transient growth studies and an estimation of optimal perturbations have been made for the compressible plane Couette flow with three-dimensional disturbances. The steady mean flow is characterized by a nonuniform shear rate and a varying temperature across the wall-normal direction for an appropriate perfect gas model. The maximum amplification of perturbation energy over time, Gmax, is found to increase with increasing Reynolds number Re, but decreases with increasing Mach number M. More specifically, the optimal energy amplification Gopt (the supremum of Gmax over both the streamwise and spanwise wave numbers) is maximum in the incompressible limit and decreases monotonically as M increases. The corresponding optimal streamwise wave number, αopt, is nonzero at M=0, increases with increasing M, reaching a maximum for some value of M and then decreases, eventually becoming zero at high Mach numbers. While the pure streamwise vortices are the optimal patterns at high Mach numbers (in contrast to incompressible Couette flow), the modulated streamwise vortices are the optimal patterns for low-to-moderate values of the Mach number. Unlike in incompressible shear flows, the streamwise-independent modes in the present flow do not follow the scaling law G(t∕Re)∼Re2, the reasons for which are shown to be tied to the dominance of some terms (related to density and temperature fluctuations) in the linear stability operator. Based on a detailed nonmodal energy analysis, we show that the transient energy growth occurs due to the transfer of energy from the mean flow to perturbations via an inviscid algebraic instability. The decrease of transient growth with an increasing Mach number is also shown to be tied to the decrease in the energy transferred from the mean flow (Ė1) in the same limit. The sharp decay of the viscous eigenfunctions with increasing Mach number is responsible for the decrease of Ė1 for the present mean flow.
Instability of channel flow with oscillatory wall suction/blowing
Authors: Gao Peng , Lu Xi-Yun
Published: April 2006

The stability of channel flow modulated by oscillatory wall suction/blowing is investigated using linear stability analysis together with Floquet theory based on numerical calculation and asymptotic expansion. Two typical flows with either the driven pressure gradient or the flow rate constant are considered. The basic flows subject to the oscillatory wall suction/blowing are time periodic with multiple frequency components. The stability problem is formulated into a time-dependent eigenvalue problem, and the Floquet exponents are obtained using a spectral collocation method. It is revealed that the periodic wall suction/blowing induces the Stokes layer, which interacts with the disturbance shear wave and eventually affects the disturbance growth. Results show that the modulations of the oscillatory wall suction/blowing to the channel flows have a destabilizing effect and the similar stability characteristics of both the typical flows occur. Critical Reynolds numbers and wave numbers are predicted for a wide range of parameters. Asymptotic expansions of the growth rate at small amplitude Δ of the oscillatory wall suction/blowing are developed. The correction terms for the growth rate occur in O(Δ2) and are positive, indicating that the flow is destabilized. It is found that the destabilizing effect is mainly connected to the steady corrections of the mean flow profile in the O(Δ2) terms.
Mechanisms of thermally induced dewetting of ultrathin silicon-on-insulator
Authors: Sutter P. , Ernst W. , Choi Y. S. , Sutter E.
Published: April 2006

Annealing of ultrathin silicon-on-insulator drives the formation of pinholes in the Si template, which in turn triggers a dewetting of the monocrystalline Si slab that is strongly affected by its crystallographic structure. An initial phase of well-defined square openings in the Si is followed by a hierarchical sequence of more complex branched shapes of the dewetting front. Annealing temperatures of about 800°C, near the onset of significant thermally activated mass transport, drive a slow and controlled evolution that allows us to identify the mechanism underlying the dewetting and explain the spontaneous formation of well-defined Si patterns at submicron dimensions.
Superscrew dislocations in silicon carbide: Dissociation, aggregation, and formation
Authors: Ma Xianyun
Published: April 2006

An approach to precisely determine the magnitude and the sign of Burgers vectors of superscrew dislocations (including elementary screw dislocations and micropipes) in silicon carbide (SiC) single crystals has been developed. The histogram of Burgers vector values associated with micropipes follows Gaussian distribution with most possible absolute Burgers vector value of about 100Å for both 4H and 6H SiC. Superscrew dislocations are quasistable. Their transformations, such as dissociation, coalescence, and aggregation, follow the principle of Burgers vector conservation and energetically favored behavior. The coalescence of dislocations with same-sign Burgers vectors is less likely to occur during the growth. Finally, a possible mechanism of mismatched coalescence between multiple nucleation sites is proposed to understand the formation of micropipes with large Burgers vectors at the early stage of SiC bulk growth.
Effect of time-dependent piston velocity program on vortex ring formation in a piston/cylinder arrangement
Authors: Shusser Michael , Rosenfeld Moshe , Dabiri John O. , Gharib Morteza
Published: April 2006

An analytical model describing laminar vortex ring formation in a nozzle flow generator (piston/cylinder arrangement) proposed previously by the authors is extended to time-dependent velocity programs. The predictions of the model are in good agreement with the available numerical data for impulsive, linear, and trapezoidal velocity programs. We also show that properly scaled vortex circulation is another universal quantity, in addition to the dimensionless energy, related to vortex rings and verify this by comparing with available numerical simulations and experimental results.
Raman studies of Bi2CuO4 at high pressures
Authors: Zhang F. X. , Saxena S. K.
Published: April 2006

The tetragonal compound Bi2CuO4 was investigated at high pressures by using an in situ Raman scattering method. A pressure-induced structural transition started at 20GPa and completed before 37.2GPa was found. Raman measurements revealed that the above phase transition is reversible.
Fabrication and characterizations of proton-exchanged LiNbO3 waveguides fabricated by inductively coupled plasma technique
Authors: Ren Z. , Heard P. J. , Hallam K. R. , Wotherspoon Alex , Jiang Q. , Varrazza R. , Yu S.
Published: April 2006

This Letter reports the use of an inductively coupled plasma technique for fabrication of proton-exchanged (PE) LiNbO3 (LN) waveguides. Planar and stripe waveguides have been formed in Y-cut LN which are difficult to obtain with the conventional molten acid method due to the occurrence of surface damage. Secondary ion mass spectrometry, scanning electron microscopy, and infrared absorption spectrum characterization results revealed that a uniform vertical PE profile with a single low order crystal phase has been directly obtained as a result of this unique process. X-ray photoelectron spectroscopy characterization of the treated surface revealed the existence of NbO as the cause for a sometimes darkened surface and confirms the ability to completely restore the surface to LN by oxygen plasma treatment. Atomic force microscopy measurement confirms that good surface quality has been maintained after regeneration of the surface to LN.
Fabrication of robust, high-quality two-dimensional colloidal crystals from aqueous suspensions containing water-soluble polymer
Authors: Kim Mun Ho , Choi Hong Kyoon , Park O Ok , Im Sang Hyuk
Published: April 2006

In this letter, we report that two-dimensional (2D) polystyrene colloidal crystals of much higher quality can be fabricated in a single-step confined convective assembly process by introducing water-soluble polymer into the colloidal suspension. The presence of the water-soluble polymer in the aqueous phase enables the colloidal particles to arrange into more hexagonally close-packed single crystalline domains, and thus reduces the defect density. In addition, the physical stability of the final 2D colloidal crystals is improved because each particle is bonded to neighboring particles and to the substrate by polymer bridges.
Scanning frequency mixing microscopy of high-frequency transport behavior at electroactive interfaces
Authors: Rodriguez Brian J. , Jesse Stephen , Meunier Vincent , Kalinin Sergei V.
Published: April 2006

An approach for high-frequency transport imaging, referred to as scanning frequency mixing microscopy (SFMM), is developed. Application of two high-frequency bias signals across an electroactive interface results in a low-frequency component due to interface nonlinearity. The frequency of a mixed signal is chosen within the bandwidth of the optical detector and can be tuned to the cantilever resonances. The SFMM signal is comprised of an intrinsic device contribution and a capacitive mixing contribution, and an approach to distinguish the two is suggested. This technique is illustrated on a model metal-semiconductor interface. The imaging mechanism and surface-tip contrast transfer are discussed. SFMM allows scanning probe microscopy based transport measurements to be extended to higher, ultimately gigahertz, frequency regimes, providing information on voltage derivatives of interface resistance and capacitance, from which device characteristics such as Schottky barrier height, etc., can be estimated.
Controlled particle generation in an inductively coupled plasma
Authors: Schulze M. , von Keudell A. , Awakowicz P.
Published: April 2006

By injecting pulses of acetylene into an inductive argon/helium discharge, carbon clusters with diameters in the range of 10–50nm are produced. These particles cause an instability of the plasma, which becomes visible as an oscillation of the emission intensity. The particles are analyzed ex situ using atomic force microscopy and scanning electron micrographs. A unique linear dependence between particle size and oscillation time period is found. Thereby the oscillation phenomenon can serve as monitor signal to control the size of plasma produced particles.
Electric-field-induced resistance switching universally observed in transition-metal-oxide thin films
Authors: Hamaguchi M. , Aoyama K. , Asanuma S. , Uesu Y. , Katsufuji T.
Published: April 2006

We show that polarity-dependent, nonvolatile resistance switching by electric field occurs in the thin film of various transition-metal oxides in almost the same manner. This result indicates that, contrary to the general acceptance, perovskite manganite is by no means a special compound for this phenomenon. It is also suggested that the resistance switching is not dominated by a detailed electronic structure of each sample, but dominated by a more general origin, e.g., crystalline defect.
Viscous damping of microresonators for gas composition analysis
Authors: Xu Yang , Lin J.-T. , Alphenaar Bruce W. , Keynton Robert S.
Published: April 2006

The damping effect of various gas environments on a silicon, lateral microresonator implemented with piezoresistive detection is investigated in this study. The resonant frequency of the cantilever shifts due to viscous damping by an amount that is directly determined by the molar mass of the gas, thereby providing a method to determine the composition of the gas environment. In addition, the microresonator demonstrates the ability to perform CO2 composition analysis using this nonreaction based detection method. The advantages of this gas analysis method are that it is simple, repeatable, reversible and not limited to reactive gases.
Ferromagnetism in Co doped CeO2: Observation of a giant magnetic moment with a high Curie temperature
Authors: Tiwari Ashutosh , Bhosle V. M. , Ramachandran S. , Sudhakar N. , Narayan J. , Budak S. , Gupta A.
Published: April 2006

We report room temperature ferromagnetism in single crystal Ce1−xCoxO2−δ (x⩽0.05) films deposited on a LaAlO3(001) substrate. Films were grown by a pulsed laser deposition technique and were thoroughly characterized using x-ray diffraction, high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy and scanning transmission electron microscopy-Z contrast, x-ray photoelectron spectroscopy, optical transmission spectroscopy, and magnetic measurements. These films are transparent in the visible regime and exhibit a very high Curie temperature ∼740–875K with a giant magnetic moment. Our results indicate that the ferromagnetic property is intrinsic to the CeO2 system and is not a result of any secondary magnetic phase or cluster formation.