Vertical Interface Research Articles

Parallel-branch braiding of river channels: Formation conditions, morphology, and dynamics

The conditions and mechanisms of the formation of parallel-branch braidings—the least studied and most complex variety of braided channels are analyzed. They are proved to be related with the appearance of a vertical interface between water masses in rivers with weakly stable, wide, spread channel; large runoff of channel-forming (tractable) sediments. Channels of this type in the Northern Dvina and the Upper Ob are described in detail.

Evaluation of Stage-Discharge Relationship in Compound Channels

Experimental results were compared with the computed results obtained from the nine most well-known methods for computation of discharge in a compound channel. The results demonstrate a high accuracy of the divided channel method with the horizontal division lines, while the length of division line is included within the calculation of the wettd perimeter. In addition, as relative depth increases, the results of the all methods converge to each other and also in case of steeper slopes in lower relative depths, more agreements between different calculated methods and experimental results were observed. Furthermore, the results show the effects of the maximum momentum transfer on the horizontal interface between the main channel and flood plains, while further angular distance from the horizontal interface toward the vertical interface between main channel and flood plains causes gradual decrease of momentum transfer effects.

A New Method of Studying Ion Transfer at Liquid|Liquid Phase Boundaries Using a Carbon Nanotube Paste Electrode with a Redox Active Binder

We report a new method for the study of voltammetric processes at liquid vertical bar liquid interfaces, namely that of using a redox active organic oil as the binder in a carbon nanotube (CNT) paste electrode. Specifically we report voltarnmetry at the,liqui vertical bar liquid interface studied at a N,N-didodecyl-N',N'-diethylphenylenediamine (DDPD, as binder) CNT paste electrode immersed in aqueous electrolytes containing potassium salts of various anions (AsF6-, PF6_, ClO4-, SCN-, I-, NO3, Br-, Cl-, F-, and SO42-). Ion transfer across the liquid vertical bar liquid interface occurs to maintain electroneutrality upon oxidation of the DDPD, the direction of which, and the subsequent effect upon the observed voltammetric response, is found to be driven by the relative hydrophobicity of the ions involved. This method of studying liquid vertical bar liquid interfaces offers significant advantages, not least with regard to ease of electrode fabrication and cleaning and the formation of multiple three-phase boundaries (at which any voltarnmetry must occur) due to the structure of the DDPD-CNT paste vertical bar aqueous electrolyte interface.

A theoretical analysis of mixed convection in aquifer storage and recovery: How important are density effects?

Aquifer storage and recovery (ASR) involves the injection of freshwater into a confined aquifer and represents an alternative to surface water storage. This paper investigates the hydrogeologic parameters governing density effects in a mixed convection system during the injection, storage and recovery of a freshwater bubble in a saline (isotropic and homogeneous) aquifer. The vertical interface between injected freshwater and ambient saltwater is inherently unstable due to the density difference between the two fluids. This instability can potentially lead to macroscopic rotation of the interface, leading to premature breakthrough of salt at the bottom of the well and hence reduce the volume of water that is recoverable at an acceptable quality. Significance of density effects during injection was found to depend on the mixed convection ratio (a ratio of the characteristic velocities from forced convection due to pumping, to free convection due to concentration differences), with the greatest interface tilt occurring with high density contrasts plus slow injection rates and high hydraulic conductivities. During storage, the extent of the density effect depends on the storage duration and hydraulic conductivity. During recovery, the breakthrough curve shape is profoundly different in density-dominated cases compared with advection and dispersion-dominated cases. Dispersive mixing was found to attenuate density effects in all three phases of ASR. This study demonstrates that the density contrast alone is insufficient as a decision parameter when choosing whether density effects are negligible. Even when modelling ASR scenarios where the density contrast is low and would traditionally be considered negligible, the decision to include or neglect fluid density in the model should be based on a full mixed convection analysis, as considered in this study. Density effects in ASR are shown to depend on the relative influences of the density difference, hydraulic conductivity, pumping rates, injected radius, storage duration, and dispersivity.

SU-FF-T-345: Photon Dose Calculation Analysis of a Varian Treatment Planning System Algorithm On a Siemens Linear Accelerator in Inhomogeneous Media

Purpose: To analyze the accuracy of photon dose calculations in inhomogeneous media using the analytical anisotropic algorithm (AAA) and pencil beam convolution (PBC) implemented in Varian Medical Systems' Eclipse treatment planning system with Siemens linear accelerators. Method and Materials: Using a 0.125 cm3 ionization chamber in a 3-layer phantom with cork between water-equivalent layers, we measured absolute depth doses (DD) for 6 and 15 MV, and 3, 5, 10, and 20 cm square fields. To assess lateral disequilibrium modeling, we irradiated another phantom in which the middle cork layer extended laterally only 2.5 cm beyond the central axis, the remainder of the layer being plastic with 10 and 20 cm square fields. Dose profiles were measured using EDR2 film placed at three depths and with a diode detector array placed in the bottom layer. Calculations were performed using AAA and PBC with inhomogeneity correction in Eclipse. Results: For both 6 and 15 MV, the DD calculated by AAA and PBC agreed with measurement within 2% and 3%, respectively proximal to the inhomogeneity beyond the buildup region. Within the inhomogeneity, the agreement was better than 6% for large fields, however, both algorithms overestimated the dose by up to 20% (AAA) or 55% (PBC) for the 3-cm 6MV field. Distal to the inhomogeneity, AAA modeled the shape of the buildup more accurately than PBC. Lateral profiles indicated that the shape of the penumbra in the inhomogeneous region and the perturbation at the vertical interface predicted by AAA agreed with film and diode array measurements better than PBC. Conclusion: AAA offered an overall improvement over PBC in inhomogeneous media, particularly for small fields and in interface and buildup regions. The overestimate of dose within the inhomogeneity for small fields motivates further investigation, particularly if AAA is used for IMRT calculations in lung.

Diffraction of surface waves on a vertical interface

A problem of diffraction of waves on a vertical interface of media is studied. The waves are radiated by a point source. The reflected and refracted wave fields are obtained by the method of parabolic equation. The corresponding transformation coefficients are found for the Neumann boundary condition. Bibliography: 5 titles.

Computation of momentum transfer coefficient and conveyance capacity in compound channels

The momentum transfer coefficient is an important parameter for determining the apparent shear stress at the vertical interface between the main channel and its associated flood plains, the cross-sectional mean velocity and the discharge capacity in compound channels. In this article, under the Boussinesq assumption and through analyzing the characteristics of velocity distribution in the interacting region between the main channel and its associated flood plain, the expression of momentum transfer coefficient was theoretically derived. On the basis of force balance, the expression of vertical apparent shear stress was obtained. By applying the experimental data from the British Engineering Research Council Flood Channel Facility (SERC-FCF), the relationship between the momentum transfer coefficient with the relative depth and the ratio of the flood plain width to the main channel width, was established, And hence the conveyance capacity in compound channels was calculated with Liu and Dong's method. The computed results show that the momentum transfer coefficient relationship obtained is viable.

A single-scattering correction for large contrasts in elastic layers

The single-scattering solution is implemented in a formulation that makes it possible to accurately handle solid-solid interfaces with the parabolic equation method. Problems involving large contrasts across sloping stratigraphy can be handled by subdividing a vertical interface into a series of two or more scattering problems. The approach can handle complex layering and is applicable to a large class of seismic problems. The solution of the scattering problem is based on an iteration formula, which has improved convergence in the new formulation, and the transverse operator of the parabolic wave equation, which is implemented efficiently in terms of banded matrices. Accurate solutions can often be obtained by using only one iteration.

Evaluating the strength and deformation characteristics of a soil bag pile from full-scale laboratory tests

The compressive strength of a soil bag pile when compressed vertically and the shear strength when sheared laterally were evaluated by performing a series of full-scale loading tests. The effects of soil bag material, backfill soil type, number of soil bags in a pile and associated effects of the end restraint at the top and bottom ends of a soil bag pile were evaluated. The results of vertical compression tests showed that initial compaction of the backfill in the soil bags is effective in increasing the initial stiffness at small deformation, and that preloading is even more effective in increasing the overall stiffness and decreasing the creep deformation. The shear strength of a soil bag pile subjected to lateral shear is substantially smaller as compared with a high compressive strength when compressed vertically. It was found that the shear strength of well-graded granular backfill was partially mobilised in vertical compression tests but the mobilisation was even lower in the lateral shear tests. The soil bag pile showed highly anisotropic strength characteristics, resulting from no or negligible complementary shear stresses acting at the vertical interface between the horizontally adjacent soil bags and highly anisotropic reinforcing effects of geosynthetic cover sheets of soil bags.

Effectiveness of Embedded-SiGe in Strained-SOI Substrates and Implications on Embedded-SiGe Stress Transfer Mechanics

Embedded-SiGe is shown to be fully compatible with strained-SOI substrates. Despite a lack of lateral lattice mismatch between the SiGe and strained-SOI, the resulting drive current improvement from embedded-SiGe is identical for strained-SOI and standard SOI control (where a lateral lattice mismatch is present). This result isolates the vertical lattice mismatch as the source of stress generation from embedded-SiGe. The concept of a critical length of SiGe beyond the vertical Si-SiGe interface is introduced to explain the observed experimental results, and is confirmed by various SiGe epitaxial fill-height and stress relaxation experiments.

IMS service-based bearer control

With the blurring of the lines between traditional telephony services and the growing number of Internet Protocol (IP)-based services available to customers of voice- and data-service providers, there is a growing need to provide a vertical interface between the service/session layer (where the service intelligence exists) and the transport layer (which provides the bearer path for service data traffic). The communication between the service/session layer and the bearer plane is referred to in standards organizations and in this paper as service-based bearer control (SBBC). The 3rd Generation Partnership Project (3GPP), the 3rd Generation Partnership Project 2 (3GPP2), the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) Focus Group on Next Generation Networks, and other standards organizations are discussing interfaces to provide SBBC functionality. This paper addresses the requirements of the SBBC interfaces and provides information about the capabilities they provide, but it does not reflect any particular set of standards, because the standards in this area are still very much under development. Rather, it presents various issues that are being discussed and that will influence the standards that are ultimately agreed upon.

Displacement-based formulations for composite beams with longitudinal slip and vertical uplift

This paper describes three novel displacement-based formulations for the analysis of composite beams with a flexible connection which is capable of deforming along the longitudinal axis of the member as well as vertically, i.e. transverse to the interface connection. For completeness, the analytical model which forms the basis of the proposed modelling technique is presented in both its weak and strong forms. The three novel finite element formulations are derived and tested using different structural systems; their nodal freedoms include the vertical and axial displacements as well as the rotations at each element end of both layers. Curvature locking problems are observed to occur for one of these elements and the origin of this behaviour is demonstrated analytically. Two applications are then proposed adopting a bi-linear constitutive relationship for the vertical interface connection to reflect the more realistic case in which, already in the linear-elastic range of the materials forming the cross-section and of the longitudinal interface connection, two vertical connection stiffnesses are required, i.e. one to model the event of separation between the layers and one when one bears against the other one. Copyright © 2005 John Wiley & Sons, Ltd.

Nonuniform and sequential magnetization reversal via domain structure formation for multilayered system with grain size induced enhanced exchange bias

We report on the magnetization reversal in series of exchange-biased multilayers NiFe(10.0 nm)/[ Ir20Mn80(6.0 nm)/Co80Fe20(3.0 nm)] N studied by specular reflection and off-specular scattering of polarized neutrons. All specimens are sputtered and post-annealed at 530 K (i.e. above the IrMn Neel temperature of 520 K) in Ar atmosphere before cooling to room temperature in the presence of a field of 130 Oe which induces the unidirectional anisotropy. We find HEB is dependent upon the number of bilayers N as it gradually increases from 0.33 kOe for N=1 to a considerably higher value of upto ≈0.9 kOe for N=10. X-ray specular and diffuse scattering data reveal no significant variation of the lateral correlation length and only a weak dependence of the vertical rms interface roughness on N. Atomic and magnetic force microscopy, however, show a strong reduction of the grain size accompanied by distinct changes of the ferromagnetic domain structure. The enhancement of the exchange bias effect is presumably related to the shrinking of the related domain size in the antiferromagnet due to the structural evolution in the multilayers. Polarized neutron reflectometry (PNR) measurements are done at different applied fields sweeping both branches of the hysteresis loop. The spin-flip (SF) cross section of both the N=10 and 3 samples show diffusely scattered intensity appears gradually as the field approaches HEB and is most intense where the net magnetization vanishes. The disappearance of diffuse scattering in saturation indicates that the off-specular intensity is related to the reversal process. The reversal proceeds sequentially starting with the bottom (top) CoFe layer for decreasing (increasing) field and is related to the evolution of the grain size along the stack. The reversal of each CoFe layer is for both field branches due to domain wall motion. Thus as a main result, we observe a sequential and symmetric magnetization reversal in exchange-biased multilayers. The concomitant in-plane magnetization fluctuations revealed by off-specular spin-flip scattering indicate a more complex reversal mechanism than hitherto considered. Moreover, although the grain size decreases from N=3 to 10 by a factor of about four the reversal mechanism remains similar.

Giant magnetoreistance in evaporated nanometer scale Fe/W and Co/W multilayers

Giant magnetoresistance (GMR) is often studied in multilayers (MLs) composed of mutually immiscible pairs of metals. Low miscibility is expected also in Fe/W and Co/W couples where the heat of compound formation is Δ H ≈ 0. Therefore, the GMR in these types of MLs was studied in this work. The MLs were UHV e-beam deposited onto Si, number of periods being 5 or 10. The substrate temperature was kept between 70 and 200 °C. The layer thicknesses of Fe, Co and W were between 1 and 7 nm, resulting in different designs. The samples were analyzed by the X-ray diffraction, X-ray reflectivity and grazing incidence X-ray diffuse scattering. The GMR was measured in the field ≤5 T. In RT deposited samples, the GMR ratio was ≤0.6% even at 4.2 K. It could be increased by a KrF laser irradiation. A GMR enhancement was achieved by the deposition of Fe/W MLs at 190 °C. Here, the GMR ratio was 2% already at RT. At 190 °C, a structural coherency and strong lateral and vertical interface roughness correlations in the MLs were found. The increase of the GMR is explained by different factors including also the elimination of magnetic shortcuts due to well-replicated and slowly varying interface profiles.

Interface-roughness-induced broadening of intersubband electroluminescence in p-SiGe and n-GaInAs∕AlInAs quantum-cascade structures

The effect of intrasubband interface roughness scattering on intersubband transition linewidths in double-quantum-well and quantum-cascade (QC) structures is studied. In n-GaInAs∕AlInAs structures, the calculated ratios between the linewidths of the spatially vertical and diagonal transitions agree with the experimental values. In p-Si∕Si0.2Ge0.8 QC structures, the experimentally observed linewidth is a factor of 4–7 smaller than the predicted value. However, by assuming a vertical interface correlation between adjacent interfaces separated by less than ∼1.5nm, the theory reproduces the experiment. Transmission electron microscopy of the SiGe QC sample reveals this vertical correlation, supporting the model.

DISCHARGE ASSESSMENT FOR TWO STAGE MEANDERING AND STRAIGHT COMPOUND CHANNELS

ABSTRACT Discharge characteristics of compound sections composed of a rectangular main channel and one or two floodplains disposed off to its sides are analysed. A set of smooth and rough sections is studied with aspect ratio varying between 2 and 5. The assumed vertical, diagonal, and horizontal interface plains are used to separate the compound channel section to subsections, the discharge for each subsection are calculated using Manning's equation. These subsection discharges are then added to give the total discharge carried by the meandering and straight compound channels. However, all these interface planes give results that are different from the observed values. A variable-inclined interface is proposed for which apparent shear force is calculated as close to 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 a variable-inclined interface, the error between the measured and calculated discharges for the meandering compound sections is found to be the minimum when compared to that using other interfaces.

Compositional convection in the presence of a magnetic field. I. A single interface

We investigate the stability of a vertical interface separating two semi–infinite fluids with differing composition of light material and permeated by a magnetic field. Both fluids possess finite kinematic viscosity, ν , thermal diffusivity, κ , magnetic diffusivity, η , and negligible material diffusion. The stability depends on six dimensionless parameters: the Prandtl number, σ (where σ = ν / κ ), the magnetic Prandtl number, σ m = ν / η , the Chandrasekhar number, Q c, the Reynolds number, Re , and the ratios, B v, Γ of the vertical and normal components to the lateral component of field. A comprehensive study of the dependence of the stability on the parameters is made when Re is small. The presence of a horizontal magnetic field tends to reduce the growth rate of the non–magnetic modes and can also give rise to new modes of instability. The addition of a vertical component of field can completely counteract the stabilizing influence of the horizontal component. For field strengths in excess of some value dependent on σ , σ m and B v, the non–magnetic unstable mode is replaced by one of two magnetic modes, one of which is a roll aligned with the field and the other inclined to it. The helicity and α –effect of the small–scale unstable motions are also discussed.

Delayed reflection in a stratified acoustic strip

The wave propagation in an acoustic horizontal strip with height H and with Neumann condition at the lower boundary and Dirichlet condition at the upper one, is studied. The propagation velocity c is a piecewise constant function with two different values on the left and on the right of the vertical interface (simple vertical stratification of the medium). Using previous results found by Ali Mehmeti and Croc/Dermenjian on the spectral analysis of the problem, we detect a phenomenon of delayed reflection for narrow beams of waves hitting the interface with an angle of incidence large enough. That delay already estimated in the one-dimensional case by Ali Mehmeti/Régnier with analogous techniques, is materialized in dimension two by the Goos–Hänchen shift, experimentally measured by Haibel/Nimtz in 2001. Copyright © 2004 John Wiley & Sons, Ltd.

Enhanced exchange bias in ferromagnet/antiferromagnet multilayers

We study a series of NiFe(10.0nm)/[Ir20Mn80(6.0nm)/Co80Fe20(3.0nm)]N multilayers with different numbers N of bilayers grown by DC magnetron sputtering. After field-cooling, SQUID and MOKE measurements show a sizable increase of the exchange bias field with N. X-ray specular and diffuse scattering data reveal no significant variation of the lateral correlation length and only a weak dependence of the vertical rms interface roughness on N. Atomic and magnetic force microscopy, however, show a strong reduction of the grain size accompanied by distinct changes of the magnetic domain structure. We conclude that the enhancement of the exchange bias effect is related to the shrinking of the domain size in the antiferromagnet due to the structural evolution in the multilayers.

A single-scattering solution that handles large contrasts across interfaces

Single-scattering and energy-conservation approximations have both proven to be effective for solving range-dependent ocean acoustics problems. The energy-conservation approach is usually used in acoustic models since it provides greater efficiency. The single-scattering approach is more general and more promising for problems involving elastic layers. A range-dependent medium is approximated in terms of a series of range-independent regions separated by vertical interfaces. The single-scattering solution is usually implemented in terms of an iteration formula, which may diverge when there is a large contrast in the material properties across an interface. Convergence can be improved by artificially splitting a vertical interface into a series of slices with smaller contrasts. For the idealized problem of scattering from a single stair step, a significant error may be introduced by neglecting multiple scattering between slices. However, the approach should be accurate for problems involving gradual range dependence, such as sloping interfaces. [Work supported by the Office of Naval Research.]