Ripple Features Research Articles

Effect of a Local Ground and Probe Radiation on the Microwave Characterization of Integrated Inductors

Microwave characterization of an integrated inductor is often carried out with respect to a local ground reference. The measurement outcome, however, does not necessarily reproduce the behavior of the device in an actual circuit where a ground reference does not exist. Furthermore, inductor measurements can be affected by the unequal currents on the inner and outer conductors of the coaxial lines internal to the RF probes. Such currents tend to radiate the microwave energy into the surroundings and manifest themselves as unexpected ripple and resonance features in measurement results. In this study, a measurement model is developed including both effects and is used to analyze experimental data obtained from integrated spiral inductors. A novel deembedding technique is then proposed and applied to eliminate the local ground and unequal coaxial current effects.

High-resolution mapping and backscatter studies in support of the Ripples Program

The long-term goal of the Office of Naval Research’s RIPPLES DRI is to develop the ability to predict the geometry and evolution of seabed morphology, particularly the presence or absence of ripples which have been shown to affect the sub-seabed penetration of acoustic energy. In support of the RIPPLES and SAX04 programs, high-resolution, multifrequency, multibeam mapping surveys were completed during September and October 2004 within three small areas off Destin, FL. The first survey was completed prior to Hurricane Ivan and followed the burial of minelike targets in the SAX04 field area. The second survey occurred during the SAX04 experiments approximately 6 weeks after Hurricane Ivan made landfall. Ripples were not observed in the bathymetric data from the first survey. Some small-scale features are present in the bathymetry from the second survey; however, most of the ripples generated by Hurricane Ivan had degraded by the time the survey was completed. Large-scale ripple features are present in the bathymetric data that extend off-shore from the SAX04 area. Difference maps of the pre- and post-Hurricane Ivan bathymetry and the acoustic backscatter data show remarkable evidence of sediment deposition and erosion. [Work supported by ONR Grant N00014-04-1-0624.]

Large scale modelling of oscillatory flows over a rippled bottom

Large scale models for oscillatory flows over rippled sandy bottoms require new “turbulence” closures and boundary conditions to account for the ripple scale flow. In the present study the large scale flow with the unknown flux terms is estimated by means of a standard RANS model. The simulations do not support the application of the Boussinesq viscosity approximation in wave dominated flows, but other tentative ideas on such type of modelling are confirmed. The characteristic wave wavelength average thickness of the oscillatory boundary layer is estimated as comparable to four times the ripple height. The characteristic wave wavelength average near bottom sediment concentration is estimated to be proportional to the maximum Shields number to the third power. The characteristic wave wavelength near bottom friction is suggested to be proportional to the near bottom current and wave velocity amplitude. The characteristic ripple wavelength average thickness of the oscillatory boundary layer is estimated to be comparable to the characteristic wave wavelength averaged thickness. The characteristic ripple wavelength averaged oscillatory flux terms are estimated to be much larger than the corresponding average turbulent flux terms. The ripple wavelength averaged total flux terms appear to have extrema that are associated both with the flow- and acceleration maxima.

Maui Mesosphere and Lower Thermosphere (Maui MALT) observations of the evolution of Kelvin‐Helmholtz billows formed near 86 km altitude

Small‐scale (less than 15 km horizontal wavelength) structures known as ripples have been seen in OH airglow images for nearly 30 years. The structures have been attributed to either convective or dynamical instabilities; the latter are mainly due to large wind shears, while the former are produced by superadiabatic temperature gradients. Dynamical instabilities produce Kelvin‐Helmholtz (KH) billows, which have been known for many years. However, models and laboratory experiments suggest that these billows often spawn a secondary instability that is convective in nature. While laboratory investigations see evidence of such structures, the evolution of these instabilities in the atmosphere has not been well documented. The Maui Mesosphere and Lower Thermosphere (Maui MALT) Observatory, located on Mt. Haleakala, is instrumented with a Na wind/temperature lidar that can detect dynamic or convective instabilities with 1 km vertical resolution over the altitude region from about 85 to 100 km. The observatory also includes a fast OH airglow camera, sensitive to emissions coming from approximately 82 to 92 km altitude, which obtains images every 3 s at sufficient resolution and signal to noise to see the ripples. On 15 July 2002, ripples were observed moving at an angle to their phase fronts. After a few minutes, structures appeared to form approximately perpendicular to the main ripple phase fronts. The lidar data showed that a region of dynamical instability existed from approximately 85.5 to 87 km and that the direction of the wind shear in this region was consistent with the phase fronts of the ripple features. The motion of the ripples themselves was consistent with the wind velocity at 85.9 km. Thus in this case the observed ripple motion was the advection of KH billows by the wind. The perpendicular structures were seen to be associated with the KH billows: they formed at the time when the atmosphere briefly became convectively unstable within the region where the KH billows most likely formed. Because of this and because the ripples were oriented approximately perpendicular to and moved with the billows, we speculate that they are the secondary instabilities predicted by models of KH evolution. The primary and perpendicular features were seen to decay into unstructured regions suggestive of turbulence. While the formation and decay time appear consistent with models, the horizontal wavelength of the perpendicular structures seems to be larger than models predict for the secondary instability features.

A laboratory study of formative conditions for characteristic ripple patterns associated with a change in wave conditions

AbstractA wave‐flume experiment was conducted to examine the formative condition for three types of distinctive bedforms that emerged through deformation of existing ripples due to waning wave power. They were ripple marks with: (1) a single secondary crest, (2) double secondary crests, and (3) a rounded crest. Data were analysed using two parameters, kh and d0/λ*, where k is the wave number, h is the water depth, d0 is the near‐bottom orbital diameter, and λ* is the spacing of existing ripples. The former quantity, kh, was employed as a surrogate for the degree of flow asymmetry. The result showed that ripples with secondary crests developed under a rather symmetrical flow field with kh ≳ 0·7, if d0/λ* ≲ 1·2, whereas rounded‐crest ripples emerged under asymmetrical flow field with kh ≲ 0·7, if d0/λ* ≲ −2·9 kh + 3·2. The number of secondary crests, which initially occurred in each trough, was single if d0/λ* ≳ 0·8, or double if d0/λ* ≲ 0·8. Copyright © 2004 John Wiley & Sons, Ltd.

Association of microstructural features and rippling phenomenon in 304 stainless steel gas tungsten arc welds

High speed, high magnification video microscopy has been used to investigate rippling behaviour in autogenous 304 stainless steel gas tungsten arc (GTA) welds. Images of the trailing edge of a weld pool (solid-liquid interface) were collected during the welding process. Weld ripple formation was observed and the associated solid-liquid interface velocity was measured. A distinct sequence of events was observed each time a ripple formed. This sequence of events involved apparent changes in the solid-liquid interface velocity, dendrite morphology, and dendrite growth direction. The microstructures of a group of rippled welds were examined and a number of features associated with the rippling phenomenon were identified. These features included changes in the pattern of the interdendritic constituents and changes in the solute distribution across the ripple feature. This information coupled with the video images was used to explain more fully the weld rippling phenomenon and the origins of microstructural changes associated with it. It is shown that solute redistribution occurs in the weld on a length scale associated with the ripple features.

Instability layers and airglow imaging

For over 30 years it has been recognized that atmospheric gravity waves (AGWs) in the 80–110 km region significantly perturb the basic atmospheric state, perhaps causing instability regions and subsequent turbulence. It has also been recognized for nearly as long that AGWs cause strong fluctuations in the airglow emissions that originate in this altitude region. Airglow images have been obtained since 1973, and they have shown structures that have mainly been attributed to the passage of AGWs through this region as predicted theoretically. The AGWs have been assumed to originate largely in the troposphere because of either convective activity or the flow of air over large mountain ranges. However, intensive analysis of the properties of a class of small‐scale features currently known as ripples [Taylor et al., 1997; Nakamura et al., 1999] suggests that these features are not AGWs but are rather instability features generated in situ. The basis for this hypothesis is examined in this review, and it is concluded that while there is support for the instability hypothesis as the origin of ripple features, at present the exact nature of the instabilities causing these features is not known.

Correlation between micromagnetismand the magnetic propertiesof hard–soft Fe/Co/Cu/Co/[CoFe/Ir/CoFe] sensors

We have prepared hard-soft spin-valve systems by ultra-high vacuum evaporation. These spin-valves use a CoFe 1.5nm /Ir 0.5nm /CoFe 3nm artificial ferrimagnet (AFi) as a hard magnetic layer, and a Fe/Co bilayer as a detection layer. The Fe layer presents a strong anisotropy and a small interaction with the hard magnetic layer. The AFi is fully antiparallel and is stable up to 330 Oe and 530 Oe, respectively, along the easy (bcc Fe[100]) and the hard (bcc Fe[110]) magnetization axes. These characteristics are correlated with MFM observations made under magnetic field. By increasing the field from zero, ripple features are observed along the Fe[110] axis, and above 530 Oe, 360° domain walls start to develop. Along the Fe[100] axis the ripple features are not observed, but the domain walls characterizing the switching of the AFi are still present. Such magnetic structure plays an essential role in the interaction between the soft and the hard magnetic layers of the spin-valve, which is unfavorable for sensor applications.

In Situ Atomic Force Microscope Imaging of Supported Lipid Bilayers

In situ AFM images of phospholipase A (PLA2) hydrolysis of mica-supported one- and two-component lipid bilayers are presented. For one-component DPPC bilayers an enhanced enzymatic activity is observed towards preexisting defects in the bilayer. Phase separation is observed in two-component DMPC-DSPC bilayers and a remarkable enhanced hydrolytic activity of the PLA2-enzyme for the DMPC-rich phase is seen. Furthermore, in a supported double bilayer system a characteristic ripple structure, most likely related to the formation of the Pβ′-ripple phase is observed.

In Situ Atomic Force Microscope Imaging of Supported Lipid Bilayers

In situ AFM images of phospholipase A (PLA2) hydrolysis of mica-supported one- and two-component lipid bilayers are presented. For one-component DPPC bilayers an enhanced enzymatic activity is observed towards preexisting defects in the bilayer. Phase separation is observed in two-component DMPC-DSPC bilayers and a remarkable enhanced hydrolytic activity of the PLA2-enzyme for the DMPC-rich phase is seen. Furthermore, in a supported double bilayer system a characteristic ripple structure, most likely related to the formation of the Pβ′-ripple phase is observed.

Comparison of electromagnetic theory and various approximations for computing the absorption efficiency and single-scattering albedo of hexagonal columns

The applicability of various approximations for computing the absorption efficiency and single-scattering albedo of a randomly oriented hexagonal column is tested versus electromagnetic theory. To calculate the absorption efficiency and single-scattering albedo of the hexagonal column from electromagnetic theory we used a generalization to the separation-of-variables method, which enables continuous calculation of optical properties up to size parameters of 86. We found that the asymptotic absorption efficiency is independent of particle shape, and that, as the size parameter increases, the hexagonal column tends to its asymptotic absorption value more quickly than Mie theory. The asymptotic absorption limit of the hexagonal column is calculated accurately (to within 1%) and rapidly by use of the complex-angular-momentum approximation, indicating that this approximation could be used to calculate the absorption limit of nonspherical particles. The equal-volume sphere best approximates the hexagonal column single-scattering albedo at a strongly absorbing wavelength (e.g., 11.9 microm for an ice particle). However, in the resonance region (e.g., 80 microm for an ice particle) Mie theory fails to approximate the single-scattering albedo of the hexagonal column, but as the size parameter exceeds 10 the error in the sphere approximation reduces to within 2%. At 80-microm wavelength there is a characteristic ripple structure superimposed on the hexagonal column absorption efficiency solutions between size parameters from approximately 1 to 4. The ripple structure is indicative of surface-wave interference and is similar to the sphere but less pronounced on the hexagonal column. We investigated the applicability of ray tracing for calculating the single-scattering albedo at absorbing wavelengths relevant to remote sensing of ice particles in the atmosphere and found it to be within 4% for size parameters between 3 and 42 at 3.7-microm wavelength. At mid-infrared wavelengths (e.g., 8.5 and 11.9 microm) ray tracing is within 5% of electromagnetic theory for size parameters exceeding 10. We also tested the Bryant and Latimer absorption approximation to anomalous diffraction theory by using the separation-of-variables method.

Error rate drift caused by rubbing noise in ferrite read heads

Some combinations of DDS-3 tape drive and cassette experience a rapid increase in error rate, followed by a gradual spontaneous recovery, when a section of tape is repeatedly used. This behaviour is caused by a change in the level of rubbing noise resulting from changes to the surface of the read head. This paper describes an investigation into the nature of this noise, and in particular the effect of head-tape speed on its frequency spectrum. In some cases, standing-wave vibrations in the head structure are excited by periodic ripple features that form on the surface of the ferrite read heads.

Dynamics of Polymer Interdiffusion: The Ripple Experiment.

We explore the interdiffusion of oppositely labeled triblock polystyrene chains, HDH/DHD, during welding in the melt using dynamic secondary ion mass spectroscopy (DSIMS) and specular neutron reflectivity (SNR). The HDH chains have the central portion of the chain deuterated (D) approximately 50% while the two ends (H) each have approximately 25% protonation; the DHD is oppositely labeled, but each set of chains contains about 50% deuteration. During welding, the deuterium depth profile exhibits "ripples" whose characteristic features, such as the time and molecular weight dependent shape, amplitude, and position, are very sensitive to the microscopic details of the polymer dynamics. The ripple experiment is especially sensitive to the presence, or absence, of topological constraints and anisotropic motion of chains. The current work significantly extends the molecular weight range up to 400 000. This allows greater separation of the six key ripple features used in deciphering the correct polymer dynamics model at the polymer-polymer interface. The DSIMS and SNR experimental results are compared to theoretical predictions and ripple simulations for Rouse, polymer mode-coupling, reptation (with and without tube broadening), and other phenomenological dynamics models. The six ripple characteristics were found to be perfectly correlated and convincingly consistent with the predictions of the reptation dynamics model. The ripple results are in significant disagreement with the polymer mode-coupling model proposed by Schweizer and other tubeless models. We conclude that the reptation model, proposed by DeGennes in 1971 with parallel developments by Edwards, is the correct model to describe the dynamics of polymer interdiffusion.

Analysis of dynamic spectra in ferret primary auditory cortex. I. Characteristics of single-unit responses to moving ripple spectra.

1. Auditory stimuli referred to as moving ripples are used to characterize the responses of both single and multiple units in the ferret primary auditory cortex. Moving ripples are broadband complex sounds with a sinusoidal spectral profile that drift along the logarithmic frequency axis at a constant velocity. 2. Neuronal responses to moving ripples are locked to the phase of the ripple, i.e., they exhibit the same periodicity as that of the moving ripple profile. Neural responses are characterized as a function of ripple velocity (temporal property) and ripple frequency (spectral property). Transfer functions describing the response to these temporal and spectral modulations are constructed. Temporal transfer functions are inverse Fourier transformed to obtain impulse response functions that reflect the cell's temporal characteristics. Ripple transfer functions are inverse Fourier transformed to obtain the response field, a measure analogous to the cell's response area. These operations assume linearity in the cell's response to moving ripples. 3. Transfer functions and other response functions are shown to be fairly independent on the overall level or depth of modulation of the ripple stimuli. Only downward moving ripples were used in this study. 4. The temporal and ripple transfer functions are found to be separable, in that their shapes remain unchanged for different test parameters. Thus ripple transfer functions and response fields remain statistically similar in shape (to within an overall scale factor) regardless of the ripple velocity or whether stationary or moving ripples are used in the measurement. The same stability in shape holds for the temporal transfer functions and the impulse response functions measured with different ripple frequencies. Separability implies that the combined spectrotemporal transfer function of a cell can be written as the product of a purely ripple and a purely temporal transfer functions, and thus that the neuron can be computationally modeled as processing spectral and temporal information in two separate and successive stages. 5. The ripple parameters that characterize cortical cells are distributed somewhat evenly, with the characteristic ripple frequencies ranging from 0.2 to > 2 cycles/octave and the characteristic angular frequency typically ranging from 2 to 20 Hz. 6. Many responses exhibit periodicities in the spectral envelope of the stimulus. These periodicities are of two types. Slow rebounds, not found in the spectral envelope, and with a period of approximately 150 ms, appear with various strengths in approximately 30% of the cells. Fast regular firings with interspike intervals of approximately 10 ms are much less common and appear to correspond to interactions between the component tones that make up a ripple.

Investigation of the Incorporation of Amphiphilic Model Peptides in Model Membranes

Amphiphilic oligopeptides containing a hydrophobic α-helical amino acid sequence were prepared and studied with respect to their ability to be integrated into the lipid double layer of phospholipid liposomes. The incorporation of the amphiphilic peptides was determined from the disturbance of the characteristic ripple phase of liposomes by means of freeze-fracture electron microscopy, from the decrease in mobility of fluorophoric groups by means of fluorescence anisotropy decay measurements, and from the formation of porous areas in black lipid membranes.

Computer simulations of self-organized wind ripple patterns

A variety of surficial patterns including beach cusps, sand dunes, wind ripples, stone stripes and sorted circles have been reproduced successfully with computer simulations in which the patterns develop via self-organization and both transporting agents and transported material are discretized. As an example, three-dimensional, grain-level computer simulations of wind ripple formation are described. The results of these simulations demonstrate that a model that includes only incremental transport of surface grains by impacts from wind-propelled hopping (saltating) grains is sufficient to produce self-organized wind ripples whose size, cross-sectional shape, plan-view geometry and time evolution from an original flat surface fall within observed ranges for natural ripples. Simulated wind ripples are initiated from a flat sand bed because of an instability deriving from a dependence of transport rate on slope. A characteristic ripple spacing that is proportional to the grain diameter and increases slowly with time develops as a result of interactions and mergers between ripples. Imperfections to the ripple pattern play a significant role in the determination and evolution of the spacing of simulated ripples.

A two-stage micromechanics model for short fatigue cracks: Hussain, K., De Los Rios, E.R. and Navarro, A. Eng. Fract. Mech. (Feb. 1993) 44 (3), 425–436

The effect of slip amplitude on the fretting fatigue behaviour of several alloy steels was investigated. Fretting fatigue experiments were conducted on flat fretting junctions under axial tension at a stress ratio of 0.1, with fretting surfaces of the same material. At a normal pressure of 24.5 MPa, the fretting fatigue lives of 2Cr13 and 35CrMo (quenched, tempered for 2 h and air cooled) show a minimum value at a slip amplitude of about 20 μm. At a normal pressure of 49 MPa, the fretting fatigue lives of 35CrMo (quenched, tempered for 2 h and air cooled) steel decrease with increasing slip amplitude. In the range of elastic slip, the variations of tangential stress and alternating stress are in phase, i.e. the fretted area experiences proportional loading. In the range of macro-slip, the variations of tangential stress and alternating stress are out of phase owing to the occurrence of stick-slip movement, so the fretted area experiences non-proportional loading. When the normal pressure is 49 MPa, the fretted areas show ripple features at slip amplitudes of 10 μm. With increasing slip amplitude, the depth of wear scars increases and wear damage becomes more severe. At slip amplitudes of above 45 μm, adhesive transfer occurs between the fretting-damaged surfaces of 2Cr13 specimens, while abrasive ploughing takes place between the fretting-damaged surfaces of 35CrMo and 60Si2Mn specimens.

Effect of slip amplitude on fretting fatigue

The effect of slip amplitude on the fretting fatigue behaviour of several alloy steels was investigated. Fretting fatigue experiments were conducted on flat fretting junctions under axial tension at a stress ratio of 0.1, with fretting surfaces of the same material. At a normal pressure of 24.5 MPa, the fretting fatigue lives of 2Cr13 and 35CrMo (quenched, tempered for 2 h and air cooled) show a minimum value at a slip amplitude of about 20 μm. At a normal pressure of 49 MPa, the fretting fatigue lives of 35CrMo (quenched, tempered for 2 h and air cooled) steel decrease with increasing slip amplitude. In the range of elastic slip, the variations of tangential stress and alternating stress are in phase, i.e. the fretted area experiences proportional loading. In the range of macro-slip, the variations of tangential stress and alternating stress are out of phase owing to the occurrence of stick-slip movement, so the fretted area experiences non-proportional loading. When the normal pressure is 49 MPa, the fretted areas show ripple features at slip amplitudes of 10 μm. With increasing slip amplitude, the depth of wear scars increases and wear damage becomes more severe. At slip amplitudes of above 45 μm, adhesive transfer occurs between the fretting-damaged surfaces of 2Cr13 specimens, while abrasive ploughing takes place between the fretting-damaged surfaces of 35CrMo and 60Si2Mn specimens.

A study of the early stages of erosion of 1100 aluminum using a mechanical properties microprobe

The incubation period during erosion of 1100 Al has been studied by monitoring the changes occurring in the immediate subsurface layers using a mechanical properties microprobe. The results show that the very near surface regions reach maximum hardness well before steady state, concurrent with the development of a characteristic surface ripple structure. This is interpreted as support for models of material removal in steady state based on some form of critical strain criteria rather than a fracture flow stress. It is also observed that material under valleys in the ripple structure is hardened to shallower depths. The significance of this result is not yet clear but appears to be linked to the development of the ripple structure.

Ripple induced diffusion of fast ions in tokamaks with an elliptic cross-section

The diffusion of high energy ions caused by toroidal magnetic field ripple in a tokamak with flux surfaces of elliptical cross-section is studied. It is shown that the elongation of the cross-section increases the characteristic ripple value above which the collisionless motion of the trapped particles becomes stochastic. The elongation also results in a reduction of the diffusion coefficient, both in the regime of collisionless (intrinsic) stochasticity and in various collisional regimes. It is further shown that in an elliptical tokamak the energy range in which the weak collision regime is achieved is narrowed, and the range characterized by ripple-plateau diffusion is broadened. The distribution of the fast ion flux to the wall is also considered.