Trend In Amplitude Research Articles

Turbidity suppression from the ballistic to the diffusive regime in biological tissues using optical phase conjugation

We describe the amplitude and resolution trends of the signals acquired by turbidity suppression through optical phase conjugation (TSOPC) with samples that span the ballistic and diffusive scattering regimes. In these experiments, the light field scattered through a turbid material is written into a hologram, and a time-reversed copy of the light field is played back through the sample. In this manner, the wavefront originally incident on the sample is reconstructed. We examine a range of scattering samples including chicken breast tissue sections of increasing thickness and polyacrylamide tissue-mimicking phantoms with increasing scattering coefficients. Our results indicate that only a small portion of the scattered wavefront (<0.02%) must be collected to reconstruct a TSOPC signal. Provided the sample is highly scattering, all essential angular information is contained within such small portions of the scattered wavefront due to randomization by scattering. A model is fitted to our results, describing the dependence of the TSOPC signal on other measurable values within the system and shedding light on the efficiency of the phase conjugation process. Our results describe the highest level of scattering that has been phase conjugated in biological tissues to date.

Velocity analysis using AB semblance

ABSTRACTI derive and analyse an explicit formula for a generalized semblance attribute, which is suitable for the velocity analysis of prestack seismic gathers with distinct amplitude trends. While the conventional semblance can be interpreted as a squared correlation with a constant, the AB semblance is defined as a correlation with a trend. This measure is particularly attractive for analysing class II AVO anomalies and converted waves. Analytical derivations and numerical experiments show that the resolution of the AB semblance is approximately twice as low as that of the conventional semblance. However, this does not prevent it from being an effective attribute. I use synthetic and field data examples to demonstrate the improvements in velocity analysis from AB semblance.

Does Trochanteric Step Osteotomy Provide Greater Stability Than Classic Slide Osteotomy? A Preliminary Study

The use of a trochanteric slide osteotomy needs a partial weightbearing period to allow safe healing of the osteotomy. We compared the initial rigidity of fixation of the trochanteric slide osteotomy with that of a newly developed technique, the trochanteric step osteotomy. The slide and step osteotomies were tested on six bilateral pairs of cadaveric femora with cyclic shear load of constant amplitude for 100 cycles in both a superior direction to represent standing and 60 degrees of hip flexion to represent a squat stance. Translational and rotational migration and cyclic amplitude were measured with an optoelectronic camera system. During superior loading, translational migration of the slide osteotomy was greater than for the step osteotomy (slide median, 1.7 mm; step median, 0.3 mm), but rotational migration was not (slide median, 1.9 degrees; step median, 0.2 degrees ). Translational amplitude was greater for the slide osteotomy in the superior direction (median slide, 0.3 mm; median step, 0.16 mm), but not in rotational amplitude. Similar trends in migration and amplitude were observed for the squat loading configuration. The data suggest the trochanteric step osteotomy is a more stable construct than the commonly performed slide osteotomy.

Sound generation on bubble coalescence following detachment

A system in which bubbles coalesced on formation was used to probe one mechanism by which bubbles create sound. The aim was to determine in which situations sound is produced and to predict its amplitude. A set of carefully co-ordinated high-speed video and acoustic timeseries showed that needle-formed bubbles generated loud bubble-acoustic emissions at the instant of coalescence of secondary bubbles with the primary bubble. As the air flow rate increased, the size and number of secondary bubbles increased, and the sound amplitude also increased. On coalescence, the sound pressure always rose initially. A dimensionless scaling found that the sound amplitude emitted scaled with the volume of the secondary bubble. This scaling was shown to be consistent with the sound-emission mechanism being the equalization of pressures in the coalescing bubbles. The trend in amplitude with bubble production rate was well predicted by the scaling.

Sulfur dioxide emissions and degassing behavior of Erebus volcano, Antarctica

Emission rates of sulfur dioxide (SO 2) were measured at Erebus volcano, Antarctica in December between 1992 and 2005. Since 1992 SO 2 emissions rates are normally distributed with a mean of 61 ± 27 Mg d − 1 (0.7 ± 0.3 kg s − 1 ) ( n = 8064). The emission rates vary over minutes, hours, days and years. Hourly and daily variations often show systematic and cyclic trends. Long-wavelength, large amplitude trends appear related to lava lake area and both are likely controlled by processes occurring at depth. Time series analysis of continuous sequences of measurements obtained over periods of several hours reveals periodicity in SO 2 output ranging from 10 to 360 min, with a 10 min cycle being the most dominant. Closed and open-system degassing models are considered to explain observed variable degassing rates. Closed-system degassing is possible as rheological stiffening and stick/slip may occur within the system. However, the timescales represented in these models do not fit observations made on Erebus. Open-system degassing and convection fits the observations collected as the presented models were developed for a system similar to Erebus in terms of degassing, eruptive activity and process repose time. We show that with the observed emission rate (0.71 kg s − 1 ) and a crystal content of 30%, magma will cool 65 °C to match observed heat fluxes; this cooling is sufficient enough to drive convection.

Evolution of pion HBT radii from RHIC to LHC— predictions from ideal hydrodynamics

We present hydrodynamic predictions for the charged pion HBT radii for a range of initial conditions covering those presumably reached in Pb+Pb collisions at the LHC. We study central (b = 0) and semi-central (b = 7 fm) collisions and show the expected increase of the HBT radii and their azimuthal oscillations. The predicted trends in the oscillation amplitudes reflect a change of the final source shape from out-of-plane to in-plane deformation as the initial entropy density is increased.

Sound generated by instability wave/shock-cell interaction in supersonic jets

Broadband shock-associated noise is an important component of the overall noise generated by modern airplanes. In this study, sound generated by the weakly nonlinear interaction between linear instability waves and the shock-cell structure in supersonic jets is investigated numerically in order to gain insight into the broadband shock-noise problem. The model formulation decomposes the overall flow into a mean flow, linear instability waves, the shock-cell structure and shock-noise. The mean flow is obtained by solving RANSequations with a k-ε model. Locally parallel stability equations are solved for the shock structure, and linear parabolized stability equations are solved for the instability waves. Then, source terms representing the instability wave/shock-cell interaction are assembled and the inhomogeneous linearized Euler equations are solved for the shock-noise.Three cases are considered, a cold under-expanded Mj = 1.22 jet, a hot under-expanded Mj = 1.22 jet, and a cold over-expanded Mj = 1.36 jet.Shock-noise computations are used to identify and understand significant trends in peak sound amplitudes and radiation angles. The peak sound radiation angles are explained well with the Mach wave model of Tam &amp; Tanna J. Sound Vib. Vol. 81, 1982, p. 337). The observed reduction of peak sound amplitudes with frequency correlates well with the corresponding reduction of instability wave growth with frequency. However, in order to account for variation of sound amplitude for different azimuthal modes, the radial structure of the instability waves must be considered in additionto streamwise growth. The effect of heating on the Mj = 1.22 jet is shown to enhance the sound radiated due to the axisymmetric instability waves while the other modesare relatively unaffected. Solutions to a Lilley–Goldstein equation show that soundgenerated by ‘thermodynamic’ source terms is small relative to sound from ‘momentum’ sources though heating does increase the relative importance of the thermodynamic source. Furthermore, heating preferentially amplifies sound associated with the axisymmetric modes owing to constructive interference between sound from the momentumand thermodynamic sources. However, higher modes show destructive interference between these two sources and are relatively unaffected by heating.

Long-term variations of the mesospheric wind field at mid-latitudes

Abstract. Continuous MF radar observations at the station Juliusruh (54.6° N; 13.4° E) have been analysed for the time interval between 1990 and 2005, to obtain information about solar activity-induced variations, as well as long-term trends in the mesospheric wind field. Using monthly median values of the zonal and the meridional prevailing wind components, as well as of the amplitude of the semidiurnal tide, regression analyses have been carried out with a dependence on solar activity and time. The solar activity causes a significant amplification of the zonal winds during summer (increasing easterly winds) and winter (increasing westerly winds). The meridional wind component is positively correlated with the solar activity during summer but during winter the correlation is very small and non significant. Also, the solar influence upon the amplitude of the semidiurnal tidal component is relatively small (in dependence on height partly positive and partly negative) and mostly non-significant. The derived trends in the zonal wind component during summer are below an altitude of about 83 km negative and above this height positive. During the winter months the trends are nearly opposite compared with the trends in summer (transition height near 86 km). The trends in the meridional wind components are below about 85 km positive in summer (significant) and near zero (nonsignificant) in winter; above this height during both seasons negative trends have been detected. The trends in the semidiurnal tidal amplitude are at all heights positive, but only partly significant. The detected trends and solar cycle dependencies are compared with other experimental results and model calculations. There is no full agreement between the different results, probably caused by different measuring techniques and evaluation methods used. Also, different heights and observation periods investigated may contribute to the detected differences.

An elastic, plastic, viscous model for slow shear of a liquid foam

We suggest a scalar model for deformation and flow of an amorphous material such as a foam or an emulsion. To describe elastic, plastic and viscous behaviours, we use three scalar variables: elastic deformation, plastic deformation rate and total deformation rate; and three material-specific parameters: shear modulus, yield deformation and viscosity. We obtain equations valid for different types of deformations and flows slower than the relaxation rate towards mechanical equilibrium. In particular, they are valid both in transient or steady flow regimes, even at large elastic deformation. We discuss why viscosity can be relevant even in this slow shear (often called "quasi-static") limit. Predictions of the storage and loss moduli agree with the experimental literature, and explain with simple arguments the non-linear large amplitude trends.

On detecting a trend in the residual circulation from observations of column HCl

Ground‐based measurements show that the HCl column at middle latitudes varies seasonally with a late spring maximum and a minimum in late summer. HALOE measurements of HCl profiles show that this seasonal cycle in the column is controlled by the seasonal variations of the mass and composition of the lowermost stratosphere. The seasonal maxima are produced by wintertime downward transport of stratospheric air. We hypothesize that the amplitude of the seasonal cycle is quantitatively related to the strength of the stratospheric residual circulation and stratosphere‐troposphere exchange (STE). We investigate this relationship using a multi‐decadal simulation from the GSFC Chemistry and Transport Model driven by output from a general circulation model in which an STE trend exists. We also examine the ground‐based record of HCl measurements at Jungfraujoch for evidence of a trend in the HCl seasonal amplitude that would be a signature of a long‐term change in the stratospheric circulation.

Large‐scale spatial and temporal patterns in population dynamics of the stoat, Mustela erminea, and the least weasel, M. nivalis, in Finland

The stoat and the least weasel are specialist predators of small rodents, and therefore their numbers are likely to depend on the availability of voles. These small predators are ecologically alike, but they differ somewhat in their diet. The stoat is larger in size than the least weasel and therefore capable of using a wider variety of prey species, while the least weasel is more restricted to small mammals. Voles in northern Fennoscandia exhibit cyclic dynamics of 3–5 years with large‐scale spatial synchrony and geographical trends in cycle length and amplitude. We predicted that the cyclic dynamics of voles are reflected in the dynamics of their predators with slight differences between the stoat and the least weasel. In this study we use snow‐tracking data to characterize the dynamics of small mustelids. The data were collected from different parts of Finland using permanent triangle‐shaped census routes of 12 km in 1989 to 2003. Population fluctuations of small mustelids were generally multiannually periodic and in synchrony over large areas, but we did not find any clear geographical gradient in the attribute of small mustelid dynamics comparable to those observed in vole population fluctuations. Instead, we found a similar decreasing temporal trend in the abundances of both species as has been recently reported for voles.

Hydroacoustic events located at the intersection of the Atlantis (30°N) and Kane (23°40′N) Transform Faults with the Mid‐Atlantic Ridge

We investigate the characteristics of T‐phase events located at the ends of two segments of the Mid‐Atlantic Ridge. Our motivations for the study were to understand whether T‐phase locations represent earthquake epicenters (and thus whether accurate geological inferences can be made from their spatial patterns) and to understand further the relationship between T‐phase event characteristics and earthquake properties. We examine the characteristics of 158 T‐phase events with respect to both event location water depth and source to receiver distance. The propagation paths of the T‐phases are also modeled to study the effects of encountering seafloor topography. We find that existing models for T‐phase excitation and propagation cannot explain adequately all of our observations. The amplitudes (Received Levels) of T‐phases at the hydrophones show no dependence on event water depths, in contrast to current excitation models which predict a decrease in event magnitude with increasing water depth. The Received Levels are observed to decrease with increasing source to receiver distance, and events from the two study areas exhibit different trends in relative Received Levels between hydrophones, once attenuation is taken into account. Our acoustic ray trace model is able to reproduce similar trends in relative amplitudes at the hydrophones based on 1‐D topography between the event and each hydrophone, but the variances in both the observed data and model are high. We observe a pattern of short T‐phase onset times for shallow water events and long onset times for deep water events, where onset time is defined as the time interval between the appearance of the T‐phase envelope above the ambient noise and its first peak. This suggests that the onset time may be a function of several variables, including efficiency of energy conversion based on local topography, efficiency of propagation based on event water depth, and hypocentral depth in the crust. The results of this study underscore the complexity of T‐phase excitation and propagation and argue that current models of T‐phase excitation and propagation need to be improved to explain the observed characteristics of T‐phase data.

Relay ramp evolution and mass flow deposition (Upper Kimmeridgian–Lower Volgian) in the Tail End Graben, Danish North Sea

ABSTRACTThe Central Graben in the Danish North Sea sector consists of a series of N–S to NW–SE trending, eastward‐tilted half‐grabens, bound to the east by the Coffee Soil Fault zone. This fault zone has a complex Jurassic history that encompasses at least two fault populations; N–S to NNW–SSE striking faults active in the Late Aalenian–Early Oxfordian, and NNW–SSE to WNW–ESE striking faults forming in Late Kimmeridgian time (sensu gallico), following a short period of tectonic quiescence. Sediment transport across the Coffee Soil Fault zone was controlled by fault array evolution, and in particular the development of relay ramps that formed potential entry points for antecedent drainage systems from the Ringkøbing–Fyn High east of the rift. Fault and isochore trends of the Upper Kimmeridgian–Lower Volgian succession in the northeast Danish Central Graben show that accommodation space was initially generated close to several minor, isolated or overlapping faults. Subsidence became focused along a few master faults in the Early Volgian through progressive linkage of selected faults. Seismic time isochore geometries, seismic facies, amplitude trends and well ties indicate the presence of coarse clastic lithologies locally along the fault zone. The deposits probably represent submarine mass flow deposits supplied from footwall degradation and possibly also from the graben hinterland via a relay ramp. The latter source appears to have been cut off as the relay ramp was breached and the footwall block are uplifted. Fault growth and linkage processes thus controlled the spatial and temporal trends of accommodation space generation and sediment supply to the rift basin.

Long-term observations of mean winds and tides in the upper mesosphere and lower thermosphere above Scott Base, Antarctica

Analysis of monthly mean wind velocities from a medium frequency (MF) radar at Scott Base (78°S, 167°E), Antarctica, are presented. The radar has been measuring winds in the upper mesosphere and lower thermosphere region since December 1982. Previous work related to this instrument focused on only small portions of the larger dataset. The present study examines changes in the full dataset with respect to phenomena associated with multi-year periods, namely the quasi-biennial oscillation (QBO) and the solar cycle, and long-term trends. No relationship between these phenomena and the mean winds observed are identified. A negative correlation between the amplitude of the semi-diurnal tide and solar activity is found, similar to other mesosphere and lower thermosphere observations. This correlation is also observed for the diurnal tide to a lesser extent. Other observations have usually indicated negative trends in tidal amplitudes, however, a positive trend is found in tidal amplitudes at Scott Base since 1987. Processes that could lead to explanations for the observed seasonal variations, solar cycle dependence and the amplitude trend of the tides are discussed.

Orientational dynamics of water confined on a nanometer length scale in reverse micelles

The time-resolved orientational anisotropies of the OD hydroxyl stretch of dilute HOD in H(2)O confined on a nanometer length scale in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles are studied using ultrafast infrared polarization and spectrally resolved pump-probe spectroscopy, and the results are compared to the same experiments on bulk water. The orientational anisotropy data for three water nanopool sizes (4.0, 2.4, and 1.7 nm) can be fitted well with biexponential decays. The biexponential decays are analyzed using a wobbling-in-a-cone model that involves fast orientational diffusion within a cone followed by slower, full orientational relaxation. The data provide the cone angles, the diffusion constants for motion within the cones, and the final diffusion constants as a function of the nanopool size. The two processes can be interpreted as a local angular fluctuation of the OD and a global hydrogen bond network rearrangement process. The trend in the relative amplitudes of the long and short exponential decays suggest an increasing rigidity as the nanopool size decreases. The trend in the long decay constants indicates a longer hydrogen bond network rearrangement time with decreasing reverse micelle size. The anisotropy measurements for the reverse micelles studied extrapolate to approximately 0.33 rather than the ideal value of 0.4, suggesting the presence of an initial inertial component in the anisotropy decay that is too fast to resolve. The very fast decay component is consistent with initial inertial orientational motion that is seen in published molecular-dynamics simulations of water in AOT reverse micelles. The angle over which the inertial orientational motion occurs is determined. The results are in semiquantitative agreement with the molecular-dynamics simulations.

Atomization characteristics on the surface of a round liquid jet

Fundamental mechanisms of liquid jet breakup are identified and quantified. The quality of the atomization of liquids is an important parameter of many technological processes and is, e.g. for fuels and propellants critical in defining engine performance. This investigation takes a look at the jet behavior for a single injector element to determine the influence of the injection conditions on a round liquid jet. The study focuses on the atomization of a liquid forming a classical spray. To adjust the relative velocity between the liquid jet and the gaseous ambient a wind tunnel-like coaxial flow configuration was used. This made it possible to distinguish between effects of aerodynamic forces, chamber pressure and jet velocity, which determine the liquid Reynolds number and thereby the internal jet turbulence. Shadowgraphy and a novel image-processing approach was used to determine the jet surface characteristics: wavelength and amplitude. The absolute injection velocity of the jet seems to affect the structures the most with an increasing velocity causing the wavelengths to be smaller. An increase in chamber pressure seemed to have little influence on the jet with no relative velocity between the gas and liquid jet, but increased the amplitude and drop formation frequency at other testing conditions with relative motion. The wave amplitude trends provide information about the likelihood of drop formation but are limited in maximum size due to this breakup phenomenon of the jet. The study of the direction of the relative velocity demonstrated that injector performance cannot simply be described by scalar geometrical and operational injection parameters (e.g., We , Re or Oh), but has to include the injection direction of the atomizing fluids in relation to each other and to the ambient (e.g., combustion chamber). The undisturbed jet length and the spread angle were investigated, and a correlation for the droplet separation position was proposed. The data led to an extended classification of liquid jet breakup regimes. Large wave instabilities were experimentally analyzed and compared with linear stability theory.

Log-curve amplitude slicing: Visualization of log data and depositional trends in the Middle Devonian Traverse Group, Michigan basin, United States

Well-log-curve shapes and amplitude trends are routinely used to correlate and map formations and reservoirs across petroleum basins or fields. However, the pattern-matching methods typically employed for correlation fail to make full use of the vertical resolution of well-log curves. A new technique, log-curve amplitude slicing, facilitates correlation by automating visualization of spatial trends in log-curve amplitudes. This new technique can be used with any type of log data that is sampled at a regular interval between two distinct correlated surfaces. The method generates a series of subhorizontal slices through the log curves that can be gridded and contoured to show trends and patterns in log-curve amplitudes in map view. The slices represent approximate time lines and are relative chronostratigraphic surfaces. When appropriate logs are used, the slices show the inferred distribution of lithofacies at the time of deposition. The evolution of an area can be investigated by stepping through a series of slices. Application of the log-curve amplitude-slicing technique facilitates correlation because it highlights trends that are not apparent using traditional methods to display and compare log curves.As an example of the log-curve amplitude-slicing technique, gamma-ray log data are used in this article to analyze the evolution of the Michigan basin (United States) during deposition of the Middle Devonian Traverse Group. The Traverse Group consists mostly of carbonates, but the location, relative timing, and extent of significant fine-grained clastic influx to the basin is readily identifiable when the basin's history is reconstructed using the log-curve amplitude-slicing technique.

Modeling GPR radiation and reflection characteristics for a complex temperate glacier bed

We demonstrate that ground penetrating radar (GPR) reflection data from a temperate glacier are accurately modeled using a Helmholtz‐Kirchhoff diffraction integration technique that incorporates the radiation characteristics of point dipoles on a half‐space interface. This is accomplished by comparing field data to simulated data. Our 40‐MHz field data are from a 100 × 340 m (x‐ and y‐dimensions, respectively) survey grid containing 51 parallel survey lines. The field data were collected with the dipole oriented perpendicular to the survey line (x‐dipole). The synthetic data used isotropic, x‐dipole, and y‐dipole antennas, and reflections were calculated using a bed topography previously defined by 3D Kirchhoff migration. The comparisons between the real and synthetic waveforms show excellent agreement, including reflection arrival times, amplitude trends, interference patterns, and false layering from out‐of‐plane reflections. The location of reflectors determined from exploding reflector rays explains that bed reflections rapidly sink below background noise levels when reflections originate in the antenna's E‐plane. This occurs in both the simulated data and field data. Our results are of general importance for radio‐glaciology because they demonstrate that inappropriate dipole orientation with respect to the specular reflection point can lead to more than 12‐dB reduction in bottom reflection strength. Furthermore, a complicated bottom topography readily generates secondary, out‐of‐plane reflections that are easily confused with basal till layers.

DETECTING LONG-TERM TRENDS IN TURBO-GENERATOR STATOR END-WINDING VIBRATIONS THROUGH NEURAL NETWORK MODELLING

The accurate assessment of remaining useful life based on condition monitoring variables is not a trivial task, since long-term trends are often obscured by short-term fluctuations. Short-term variations in such variables also tend to overshadow the long-term drift in magnitude. Stator end-winding vibrations are one of the key indicators of the remaining useful life of turbo-driven generators. In this paper, a technique is developed to separate long-term drifts in stator end-winding vibrations from short-term fluctuations. The technique rests on the fact that short-term variations in winding vibrations are largely affected by operational variables measured on a turbo generator, including load and temperature. These dependencies can be captured in a model reflecting the short-term behaviour of the vibration amplitudes. The long-term trend in vibration amplitude is, however, not governed by the same relationships. It is hence possible to extract the long-term trend from the overall behaviour by subtracting the short-term effects of operational variables from the overall behaviour. In this way, a reliable long-term trend is obtained, from which remaining life assessments could be made.

Observations of low‐frequency electromagnetic plasma waves upstream from the Martian shock

We have analyzed magnetic field data returned from Mars Global Surveyor (MGS) for signatures of electromagnetic plasma waves upstream from the Martian bow shock. We discuss two recurring wave features in the data. Left‐hand polarized waves (0.04–0.10 Hz) observed near the local proton gyrofrequency (PCWs) propagate at small to moderate angles to the magnetic field and have amplitudes that decrease with distance from Mars. They are concentrated in two locations upstream of the Martian shock. PCWs were reported from Phobos 2 observations and can be attributed to solar wind pickup of Mars' hydrogen exosphere. Higher‐frequency waves (0.4–2.3 Hz) are observed when MGS is magnetically connected to the Martian shock. These waves have not been reported at Mars before, but have been reported at many solar system bodies, and are attributed to whistler waves generated at the shock and propagating upstream. The sense of polarization (left‐handed or right‐handed) of the whistler waves observed in the spacecraft frame depends upon the angle between the magnetic field and the solar wind flow direction. The whistler waves at Mars follow the trends in frequency, amplitude, propagation angle, and eccentricity observed at other solar system bodies.