Vertical Interface Research Articles

Conveyance in a two-stage meandering channel with a mobile bed

A series of experiments are reported on the conveyance of over-bank mobile bed meandering channels, using the UK Flood Channel Facility at HR Wallingford. The sides of the inner channel were fixed whilst the bed was formed of graded material with a d50 of 1.6 mm. The floodplains were either smooth or, for most experiments, artificially roughened using expanded metal strips. Three floodplain planforms were used, these being straight, sinuous and narrow berms parallel to the inner channel. Inner channel discharges were measured using integrated point values from a 3-D Acoustic Doppler Velocimeter. Most discharge calculation methods for meandering channels employ a horizontal division between the main channel and floodplain meander zone. The results of several of these were compared with the observed data and were shown to be unsatisfactory when the floodplain is rough. This led to the development of a method using vertical interfaces between the inner channel and floodplains, based upon a force momentum flux balance for the inner channel. This vertical interface method is shown to give improved results for both total and sub-sectional discharges in cases where the floodplain is rough.

Direct current electric potential in an anisotropic half‐space with vertical contact containing a conductive 3D body

Detailed studies of anomalous conductors in otherwise homogeneous media have been modelled. Vertical contacts form common geometries in galvanic studies when describing geological formations with different electrical conductivities on either side. However, previous studies of vertical discontinuities have been mainly concerned with isotropic environments. In this paper, we deal with the effect on the electric potentials, such as mise‐à‐la‐masse anomalies, due to a conductor near a vertical contact between two anisotropic regions. We also demonstrate the interactive effects when the conductive body is placed across the vertical contact. This problem is normally very difficult to solve by the traditional numerical methods. The integral equations for the electric potential in anisotropic half‐spaces are established. Green′s function is obtained using the reflection and transmission image method in which five images are needed to fit the boundary conditions on the vertical interface and the air‐earth surface. The effects of the anisotropy of the environments and the conductive body on the electric potential are illustrated with the aid of several numerical examples.

Water table waves in an unconfined aquifer: Experiments and modeling

Comprehensive measurements are presented of the piezometric head in an unconfined aquifer during steady, simple harmonic oscillations driven by a hydrostatic clear water reservoir through a vertical interface. The results are analyzed and used to test existing hydrostatic and nonhydrostatic, small‐amplitude theories along with capillary fringe effects. As expected, the amplitude of the water table wave decays exponentially. However, the decay rates and phase lags indicate the influence of both vertical flow and capillary effects. The capillary effects are reconciled with observations of water table oscillations in a sand column with the same sand. The effects of vertical flows and the corresponding nonhydrostatic pressure are reasonably well described by small‐amplitude theory for water table waves in finite depth aquifers. That includes the oscillation amplitudes being greater at the bottom than at the top and the phase lead of the bottom compared with the top. The main problems with respect to interpreting the measurements through existing theory relate to the complicated boundary condition at the interface between the driving head reservoir and the aquifer. That is, the small‐amplitude, finite depth expansion solution, which matches a hydrostatic boundary condition between the bottom and the mean driving head level, is unrealistic with respect to the pressure variation above this level. Hence it cannot describe the finer details of the multiple mode behavior close to the driving head boundary. The mean water table height initially increases with distance from the forcing boundary but then decreases again, and its asymptotic value is considerably smaller than that previously predicted for finite depth aquifers without capillary effects. Just as the mean water table over‐height is smaller than predicted by capillarity‐free shallow aquifer models, so is the amplitude of the second harmonic. In fact, there is no indication of extra second harmonics (in addition to that contained in the driving head) being generated at the interface or in the interior.

Scattering from a fault interface in the Coso geothermal field

Large-amplitude, secondary arrivals are modeled as scattering anomalies near the Coso, California, geothermal field. Polarization and ray tracing methods determine the orientation and location of the scattering body. Two models are proposed for the scatterer: (1) a point scatterer located anywhere in a one-dimensional (1-D), layered velocity model; and (2) a dipping interface between two homogeneous half spaces. Each model is derived by non-linear, grid search inversion for the optimal solution which best predicts observed travel times. In each case the models predict a nearly vertical scatterer southwest of stations S4 and Y4, each southeast of Sugarloaf Mountain, a large rhyolite dome. The interface model includes five unknown parameters describing the location and orientation of the interface in addition to the S-wave velocity of the half space. The S-wave velocity, 3.25 km/s, agrees with independently derived 1-D models in this area. The large amplitude, vertical impedance contrast interface coincides with steep gradients of heat flow measured near the surface and with structural boundaries observed in surface geology. The reflector is most probably the sharp boundary between the northern part of the field where there is significant fluid flow and the southern part where hydrothermal fluids are absent. The interface coincides with geological boundaries and faults recently observed in this region, most likely representing the hydrothermal barrier which channels hot fluids northward.

Microtextured substrata alter gene expression, protein localization and the shape of cardiac myocytes

Many of the experiments designed to understand fundamental principles in cardiac physiology are performed in vitro using myocytes isolated from adult or neonatal hearts. However, these cells have probably lost some of their original properties in culture prior to study. Our objective is to recapitulate cardiac myocyte structure and function by growing cells on microtextured silicone substrata produced by photolithography and microfabrication techniques. Myocytes are plated on nontextured, micropegged (5 μm high), microgrooved (parallel grooves with a depth of 5 μm) or combination (micropegged and grooved) substrata. Myocytes plated on microtextured surfaces display a change in cell shape with an increase in myofibrillar height and a decrease in cell area. This shape change did not affect the stoichiometry of the myofibrillar proteins but did elicit microenvironmental remodeling of proteins that mechanically attach the cell to its surroundings. Cells terminate in a sarcomeric striation on the vertical interface of the peg whereas on nontextured surfaces they end in long nonstriated cables. Vinculin, a focal adhesion protein, was found to decrease in expression on combination surfaces as compared to nontextured substrata. A three-dimensional microtextured substratum appears to reintroduce a more physiological microarchitecture for tissue culture that may have potential uses in biological research as well as in tissue engineering and diagnostic applications.

Chromate and Dichromate Electro-Insertion Processes into a N,N,N′,N′-Tetraoctylphenylenediamine Redox Liquid

Ion transfer processes across aqueous vertical bar organic phase boundaries are of considerable importance in biological and analytical chemistry. When driven by a potential applied to the liquid vertical bar liquid interface the ion transfer may be detected as voltammetric response, Here, a potential applied to the electrode vertical bar aqueous electrolyte vertical bar organic oil (N,N,N',N'-tetraoctylphenylenediamine, TOPD) triple interface is employed to drive anion transfer. Upon oxidation of TOPD deposited in the form of microdroplets onto the electrode and immersed in aqueous media, the transfer of monovalent anions (perchlorate) and divalent anions (sulfate, chromate, dichromate) occurs to maintain charge neutrality in the organic oil phase. Sulfate (0.1 M) as a very hydrophilic anion undergoes transfer into the organic phase at a potential positive of 0.4 V (vs. Ag/AgCl) and may be employed as an 'inert' background electrolyte, Chromate is shown to undergo electro-insertion at low concentrations down to 10 muM. Within the oil phase chromate is undergoing condensation to the more stable dichromate.

ADJOINT VARIABLE METHOD FOR THE THERMAL DESIGN OF EUTECTIC DIRECTIONAL SOLIDIFICATION PROCESSES IN AN OPEN-BOAT CONFIGURATION

A computational method for the inverse design of a directional solidification process of a near-eutectic binary alloy driven by the coupled action of buoyancy, thermocapillary, and electromagnetic convection is presented. The objective is to calculate the mold cooling/heating conditions such that a stable desired interface growth with growth velocity vf and thermal gradient G is achieved. The interface velocity vf and thermal gradient G are chosen such that a diffusion-based growth is obtained in the presence of melt convection. Morphological stability is enforced by imposing an appropriate magnitude of G/|vf|, which is determined a-priori based on the constitutional stability criterion. The design problem is posed as a functional optimization problem. The cost functional is defined so as to represent the deviation of the freezing interface thermal conditions from thermodynamic equilibrium. An appropriate continuum adjoint problem is defined such that an analytical expression for the gradient of the objective function is obtained. The conjugate gradient method coupled with the finite element solutions of the continuum direct, sensitivity, and adjoint problems is employed for solving the inverse problem. The method is demonstrated with an example of calculating the boundary thermal fluxes for the directional growth of an Sb-8.6% Ge melt in an open-boat configuration under the influence of an external horizontal magnetic field such that a stable vertical interface advances from left to right with a desired growth velocity.

Rayleigh-Lamb Waves in a Compound Wave Guide. Reflection from and Transmission Through the Vertical Interface between Media with Different Impedances

The method of superposition is used to study the first normal wave reflecting from and transmitting through the interface in a compound waveguide consisting of two rigidly joined elastic half-strips with equal width and different mechanical properties. We study how the impedances of the contacting media influence the transformation of the energy of the incident wave to those of the reflected and transmitted waves. Two cases are considered — propagating waves of higher orders appear in the reflected wavefield earlier than in the transmitted wavefield and propagating waves of higher orders appear in the transmitted wavefield earlier than in the reflected wave field. For both cases, the impedances vary so that the incident wave can propagate in both more rigid and softer media. It is shown that by increasing the impedances of the contacting media, the interface can be made more transparent

Theoretical model for particle behavior at solidifying front in electromagnetic force field

The particle migrating behavior at solidifying front is discussed in theory with the application of electromagnetic force field (EMFF), on the basis of foregone analysis of force upon particle ahead of solidifying front without electromagnetic force field. The critical solidification velocities of particle pushing/engulfment transition ahead of horizontal and vertical interface are derived respectively when a certain EMFF is applied. And the critical electromagnetic forces of particle pushing/engulfment transition ahead of horizontal and vertical interface are also derived separately when a certain solidifying velocity is given.

Flow Interaction of Meandering River with Floodplains

A series of laboratory test results are presented concerning the boundary shear stress, shear force, and discharge characteristics of compound meandering river sections composed of a rectangular main channel and one or two floodplains disposed off to its sides. Five dimensionless parameters are used to form equations representing the total shear force percentage carried by floodplains. A set of smooth and rough sections is studied with an aspect ratio varying from 2 to 5. Apparent shear forces on the assumed vertical, diagonal, and horizontal interface plains are found to be different from zero at low depths of flow and change sign with an increase in depth over the floodplain. A variable-inclined interface is proposed for which apparent shear force is calculated as zero. Equations are presented giving proportion of discharge carried by the main channel and floodplain. The equations agree well with experimental and river discharge data. Using the variable-inclined interface, the error between the measured and calculated discharges for the meandering compound sections is found to be the minimum when compared with that using other interfaces.

Influence of water saturation on horizontal and vertical motion at a porous soil interface induced by incident SV wave

Recent field observations have indicated that water saturation of soils may strongly affect the vertical ground motion. A study is therefore carried out to investigate the effect of saturation on horizontal and vertical motion at an interface of porous soils with potential contributions directed to site evaluation based on field observations of both the horizontal and vertical motion. The problem described in this paper corresponds to an SV wave incident at the interface between the overlying soil and the underlying rock formation. The soils are modeled as partially water-saturated porous material with a small amount of air inclusions, while the rock are approximately regarded as ordinary one-phase solid. Theoretical formulation is developed for the computation of amplitudes of horizontal and vertical interface motion, which are expressed as functions of the degree of saturation, the angle of incidence as well as the frequency. Numerical results are given for a typical sand to illustrate the influence of saturation on the interface motion in two directions and their ratios. The present study demonstrates that the effect of water saturation may be substantial on both the horizontal and vertical motion as well as on their ratios, implying the importance of such effects in the interpretation of field observations.

Interface study of a Co/Si/W/Si multilayer with enhanced thermal stability

The interface evolution in an amorphous Co/Si/W/Si multilayer (ML) of 150 Å nominal period processed by rapid thermal annealing (RTA) in the temperature range of 523-1273 K for 5-30 s was studied by X-ray reflectivity and diffuse scattering measurements at Cu Kα1 wavelength. The results were simulated within the Fresnel theory and the distorted-wave Born approximation. The interdiffusion and intermixing induced by RTA starts at Co/Si interfaces and takes place via an interface shift without a considerable increase of the interface roughness up to the 873K/30s RTA. A strong conformality of the interface profiles, stretching originally over the entire ML thickness in the whole interval of the interface roughness frequencies covered by the experimental scans, is reduced to about 2 ML periods. After the 1023K/30s RTA, the interface morphology is controlled by the crystallization of Co and W silicide phases leading to interface roughening. The vertical interface correlation is sensititve to the interface roughness frequency. A fast diffusion along grain boundaries leads to a complete interdiffusion and collapse of the ML on 1273K/30s RTA. Compared with a W/Si ML studied previously, the incorporation of Co layers into the ML stack enhanced the thermal stability by about 250 K. Some consequences for optical applications are discussed.

Stability of oscillatory two-phase Couette flow: Theory and experiment

The interfacial instability due to viscosity stratification is studied experimentally in a closed Couette geometry. A vertical interface is formed between two concentric cylinders with density-matched fluids of unequal viscosity. The outer cylinder is rotated with a time-harmonic motion, causing spatially periodic disturbances of the interface. The wavelengths and growth rates predicted by linear theory agree well with experimental results. Application of Fjo/rtoft’s inflection point theorem shows the neutral stability curves to be consistent with an internal instability occurring in the less viscous phase. Because the standard Floquet theory yields only time-averaged growth rates, the instantaneous behavior of the system is examined numerically. This reveals the flow to be unstable to a disturbance which has a maximum that oscillates between the interface and a location within the less viscous fluid. Surprisingly, it is found that interfacial wave amplification originates with the internal disturbance, and is not directly caused by interfacial shear. This unsteady instability may explain the growth of waves in “transient” process flows, e.g., fluids encountering changing flow geometry. It is also demonstrated that in the long wave limit the problem of steady-plus-oscillatory plate motion is simply additive. This implies that it is possible to use oscillations to stabilize steady waves over a limited range of parameter values, but only when the less viscous phase is adjacent to the moving boundary.

A complete energy conservation correction for the elastic parabolic equation

A complete energy conservation correction is derived to improve the accuracy of the elastic parabolic equation for range-dependent problems. The correction is complete in the sense that it is valid for problems involving a broad spectrum of horizontal wave numbers. It is a linear condition that associates the incident and transmitted fields on a vertical interface with arrays of point sources having the appropriate energy flux densities. It is a generalization of a complete energy conservation correction for the acoustic parabolic equation [J. Acoust. Soc. Am. 94, 975–982 (1993)].

Giant magnetoresistance dependence on the lateral correlation length of the interface roughness in magnetic superlattices

The giant magnetoresistance (GMR) observed in magnetic multilayers, is due to spin-dependent electron transport. In order to study the influence of the interface roughness on the spin-dependent scattering we produced epitaxial Fe/Cr(001) superlattices with negligible bulk scattering. The interface roughness was varied by carefully annealing the samples. The vertical and lateral interface roughness components were quantitatively determined by specular and diffuse synchrotron x-ray diffraction using anomalous scattering. We find that the magnitude of the GMR effect increases with decreasing lateral correlation length ${\ensuremath{\xi}}_{x}$ and increasing vertical roughness amplitude \ensuremath{\eta}.

Behavior of Fine Bubbles in Front of the Solidifying Interface.

In front of the solidifying interface, the solidifying boundary layer plays an important role in determining whether foreign particles could be engulfed or not by the solidifying interface. In this study, we have investigated how the boundary layer influences the behavior of the foreign particles by directly observing the behavior of fine bubbles in front of a vertical solidifying interface of the water solution. In the case of surfactant (C8H17SO3Na) water solution, bubbles in the vicinity of the solidifying interface were found to move horizontally toward the solidifying interface, and then were engulfed by it. However, this phenomenon was not observed in the case of NaCl water solution. Analysis indicated that inside the boundary layer with a surfactant concentration gradient, a surface tension gradient around the interface of the bubble and the solution was formed. We have concluded that the surface tension gradient generates a driving force on the bubble, causing the bubble to move towards the solidifying interface. Experimental results were found to be well in accord with theoretical analysis.

The formation and evolution of layered structures in porous media

Horizontally layered structures can develop in porous or partially molten environments, such as magma chambers, the early Earth's mantle, and hydrothermal systems. We have studied the generation and evolution of these horizontally layered structures in a rigid porous medium by heating a compositionally stably stratified fluid from below. Growth of a convective layer through entrainment, the formation of a vertical density interface on top of this layer and destabilization of the next layer are closely coupled. It is shown that the growth of the first convective layer stops once the thermal equilibrium is reached. Since heat (solute) transfer across the thin density interfaces becomes purely diffusive (dispersive), the separately convecting layers can persist on a compositionally dispersive timescale. While the number of layers that develop is determined by the magnitude of the thermal Rayleigh number, the final height of a newly formed layer is inversely proportional to the buoyancy ratio. Two dynamical mechanisms which lead to sudden interface disappearance determine the vertical layer scales, rather than the initial evolution toward the thermal equilibrium. Finally, the results are discussed with respect to the above mentioned geophysical scenarios.

Effect of surface roughness on magnetization reversal of Co films on plasma-etched Si(100) substrates

Co films ∼970 Å thick were deposited, simultaneously, on ten plasma-etched Si(100) substrates with various etch times t. The surface morphologies and magnetic properties of the Co films were measured by atomic force microscopy (AFM) and magneto-optic Kerr effect (MOKE) technique. The analysis of the AFM images shows that as the etch time t increased from 0 to 100 min, the vertical interface width w increased from ∼5 to ∼1400 Å; the lateral correlation length ξ increased from ∼300 to ∼10 500 Å. The MOKE measurements provided the in-plane azimuthal angular dependence of the hysteresis loops and the change of loop shapes with the surface roughness. It was found that the magnetization reversal process changed with the surface roughness. Magnetization rotation dominated the magnetization reversal for the smoothest films. As the films roughened, the domain-wall pinning set in, eventually dominating the magnetization reversal for the roughest films. Additionally, the magnetic uniaxial anisotropy in the Co films disappeared as the roughness parameters increased. It was also found from MOKE that the surface roughness strongly affected the coercivity.

Effect of surface roughness on magnetic properties of Co films on plasma-etched Si(100) substrates

Magnetic and morphological properties of ∼970-Å-thick Co films, deposited simultaneously on ten plasma-etched Si(100) substrates, were measured through the magneto-optic Kerr effect (MOKE) technique, ferromagnetic resonance (FMR), magnetic force microscopy (MFM), and atomic force microscopy. As the etch time t increased from 0 to 100 min, the vertical interface width w of Co films increased from ∼5 to ∼1400 Å; the lateral correlation length ξ, from ∼300 to ∼10 500 Å. The MOKE and FMR measurements gave the in-plane azimuthal angular dependence of the hysteresis loops and the ferromagnetic resonance absorption spectra, respectively. From MOKE and FMR, the smoother films showed uniaxial magnetic anisotropy (t⩽40 min). The uniaxial anisotropy decreased with the increase of the surface roughness and disappeared for the roughest films (t=60 and 100 min). The MOKE hysteresis loop measurements suggested that, with the increasing surface roughness, the magnetization reversal changed gradually from magnetization rotation dominated for the smoothest films to domain-wall motion dominated for the roughest films. The MFM images of the films showed anisotropic magnetic domain contrasts for the smooth film, and the subsequent fragmentation of these domains as the roughness parameters increased. This supports the results of the MOKE and FMR measurements.

Principe d'absorption limite pour l'opérateur de Maxwell dans un milieu bihomogène

We consider the Maxwell operator A that describes 3D electromagnetic wave propagation in an infinite cylindrical wave guide with a rectangular section, where the medium is made of two homogeneous parts separated by a vertical interface. The spectral analysis of this operator points out a countable family of real numbers in the spectrum called thresholds, and the resolvent operator R A (z) = ( A − z) −1, Im (z)) ≠ 0, can be extended (‘limiting absorption principle’) continuously to the lower or upper half-planes (origin excepted) in a suitable weighted L 2-topology. In particular, this continuity holds at the thresholds.