Depth-dependent Parameters Research Articles

An adaptive beamformer based on dynamic phase coherence factor for pixel-based medical ultrasound imaging.

Pixel-based beamforming realizes dynamic focusing at the pixel level with a focused beam by assuming that the received signals are composed of spherical pulses. Far-focused pixel-based (FPB) imaging was proposed to avoid artifacts around the focal depth. However, the contrast improvement is limited. We propose an adaptive weighting method based on dynamic phase coherence factor (DPCF) to improve the image contrast while preserving the speckle pattern. The phase variation is dynamically estimated based on the noise energy proportion of echo signals and it is used to calculate phase coherence weights for suppressing interference and preserving desired signals. A depth-dependent parameter is designed for DPCF to enhance the performance of noise and clutter suppression in the far-field region. We further use the subarray averaging technique to smooth the speckle texture. The proposed method was evaluated on simulated, phantom experimental, and in vivo data. Results show that, compared with the phase coherence factor (PCF) based method, DPCF respectively leads to average CR improvements by more than 60% and 24% in simulation and experiment, while obtaining an improved speckle signal-to-noise ratio. The proposed method is a potentially valuable approach to obtaining high-quality ultrasound images in clinical applications.

Surface roughness noise analysis and comprehensive noise effects on depth-dependent coherence time of NV centers in diamond

Noise is a detrimental issue for nitrogen-vacancy (NV) centers in diamond, causing line broadening and decreasing the coherence time (T2). Following our previous electric and magnetic field noise work, we investigate noise caused by the diamond surface roughness, which is a source for charge density fluctuations and incoherent photon scattering. We find that the varying surface charge density noise source is prevalent throughout the entire NV dynamical decoupling frequency range, while the photon scattering noise is almost negligible. Next, we combine the results from various noise sources to perform comprehensive analyses on T2 and how it varies with NV depth. At a given NV depth of 5 nm below a hydrogen- or fluorine-terminated surface, we find that these magnetic nuclei reduce the NV coherence time the most, followed by the surface electric field noise sources. The photon scattering and bulk magnetic field noise effects on T2 are weak compared to the varying charge density, electric dipole, and surface impurity noise. However, with oxygen surface termination, the surface electric field noise becomes comparable to the surface magnetic field noise. Our calculated values of T2,Hahn (few microseconds to ten microseconds) are in good agreement with the experimental values reported elsewhere. Finally, we calculate an anticipated signal-to-noise ratio (SNR) for NV AC magnetometry of external nuclear spins. In our simplified assessment, where some depth-dependent parameters (e.g. NV conversion efficiency) are held constant, we find that shallower NV layers should yield the best SNR, which is consistent with experimental findings.

Sandbox – creating and analysing synthetic sediment sections with R

Abstract. Past environmental information is typically inferred from proxy data contained in accretionary sediments. The validity of proxy data and analysis workflows are usually assumed implicitly, with systematic tests and uncertainty estimates restricted to modern analogue studies or reduced-complexity case studies. However, a more generic and consistent approach to exploring the validity and variability of proxy functions would be to translate a sediment section into a model scenario: a “virtual twin”. Here, we introduce a conceptual framework and numerical tool set that allows the definition and analysis of synthetic sediment sections. The R package sandbox describes arbitrary stratigraphically consistent deposits by depth-dependent rules and grain-specific parameters, allowing full scalability and flexibility. Virtual samples can be taken, resulting in discrete grain mixtures with defined parameters. These samples can be virtually prepared and analysed, for example to test hypotheses. We illustrate the concept of sandbox, explain how a sediment section can be mapped into the model and explore geochronological research questions related to the effects of sample geometry and grain-size-specific age inheritance. We summarise further application scenarios of the model framework, relevant for but not restricted to the broader geochronological community.

Analysis of consolidation of a soil layer with depth-dependent parameters under time-dependent loadings

In this paper, a Laplace transform method is proposed to solve the one-dimensional consolidation problems considering depth-dependent parameters of the soil layer, which is subjected to complicated time-dependent loadings at ground surface. The coefficient of volume compressibility and the coefficient of permeability for the soil layer are continuous functions of vertical coordinate. The solution is obtained and described in detail. The characteristics of consolidation under suddenly imposed constant loading are analysed. The results show that the excess pore pressure distribution of a soil layer with depth-dependent parameters is dissimilar to the solution Terzaghi has proposed. The characteristics of consolidation under time-dependent loadings are also analysed and the influences of depth-dependent parameters are considered. The results also suggest that the effective stress develops with time under time-dependent loading follows the trend under suddenly-imposed constant loading but exhibit certain oscillations. The oscillation amplitudes of the effective stresses don’t decrease with time. Therefore, it is inaccurate to simplify the cyclic loading to constant loading.

Quantification of vertical solid matter transfers in soils during pedogenesis by a multi-tracer approach

Vertical transfer of solid matter in soils (bioturbation and translocation) is responsible for changes in soil properties over time through the redistribution of most of the soil constituents with depth. Such transfers are, however, still poorly quantified. In this study, we examine matter transfer in four eutric Luvisols through an isotopic approach based on 137Cs, 210Pb(xs), and meteoric 10Be. These isotopes differ with respect to chemical behavior, input histories, and half-lives, which allows us to explore a large time range. Their vertical distributions were modeled by a diffusion-advection equation with depth-dependent parameters. We estimated a set of advection and diffusion coefficients able to simulate all isotope depth distributions and validated the resulting model by comparing the depth distribution of organic carbon (including 12/13C and 14C isotopes) and of the 0–2-μm particles with the data. We showed that (i) the model satisfactorily reproduces the organic carbon, 13C, and 14C depth distributions, indicating that organic carbon content and age can be explained by transport without invoking depth-dependent decay rates; (ii) translocation partly explains the 0–2-μm particle accumulation in the Bt horizon; and (iii) estimates of diffusion coefficients that quantify the soil mixing rate by bioturbation are significantly higher for the studied plots than those obtained by ecological studies. This study presents a model capable of satisfactorily reproducing the isotopic profiles of several tracers and simulating the distribution of organic carbon and the translocation of 0–2-μm particles.

Depth-Guided Deblurring

In this paper, we propose a novel image deblurring framework, which noticeably improves the effectiveness and efficiency of state-of-the-art approaches. In professional imaging with its typical shallow depth-of-field, it is challenging to estimate the exact focus distance during recording, which often implies costly re-shooting. For the correction of blurred material in post-production, there exist a few deblurring methods, which are, however, challenged by working on real camera data due to noise and the general ill-posedness of the deblurring problem itself. Since the effective out-of-focus operating range of deblurring methods is small and the blur characteristics are strongly depth-dependent, we introduce a framework where a depth map and measured lens characteristics ingest into a selection of state-of-the-art deblurring methods. Therefor, we introduce a depthdependent parameter selection concerning blur kernels and smoothing weights first. Second, using these parameters the out-of-focus areas are selectively deblurred in order to overcome the emergence of strong artifacts. The foundation for the provided evaluation is formed by a dataset with eight real images captured with a cinematic RGB plus depth camera containing multi-planar and in-scene depth-varying image content. Therein, we show visually and numerically that introducing our depth framework improves the deblurring performance and suppresses typical strong artifacts.

Effects of depth on transport of 129I in crystalline rock

In the present paper, a model for the transport of iodine through fractures in granitic rock has been developed by taking into account the variation of parameters with depth in order to investigate the effects of depth on repository performance. First, the evolution of groundwater chemistry with depth has been modeled by considering the physical and chemical conditions that vary with depth. Second, iodine–water interactions and iodine–rock interactions under groundwater-chemistry evolution with depth in crystalline rocks have been modeled using PHREEQC, with which the distribution coefficients of iodine have been numerically evaluated as a function of depth. These values and other depth-dependent parameters such as fracture aperture, groundwater velocity, and diffusion coefficients have been used in the iodine transport simulation to observe differences in the iodine concentration in the water from repositories located at 500 and 1000m depths. The results show that iodine stays within the vicinity of the repository if it is disposed of at a greater depth. The main reason is that the retention effect of matrix diffusion increases and relative contribution of advection along fractures decreases at depth due to the cubic law for the water flow velocity in fractures.

Recovery of SIMS depth profiles with account for nonstationary effects

Abstract In this work we consider a method of accounting for the nonstationary effects in recovery of SIMS depth profiles. The depth resolution function (DRF) is described by Hofmann's nonstationary MRI (mixing-roughness-information depth) model using the depth-dependent parameters. The effects in question include the nonstationary atomic mixing and development of surface roughness. A mathematical description of the nonstationary depth profiling process by the Fredholm integral equation of the first kind is proposed. The inverse problem is solved using an algorithm based on the Tikhonov regularization method. The proposed nonstationary recovery method is tested on both model and real structures. The development of surface roughness in SIMS depth profiling of the real structure was observed. Grazing incidence x-ray reflectometry (XRR) technique was used to verify the results of SIMS profiles restoration for periodic structure containing thin Ge layers in the Si matrix. The advantages of the proposed recovery algorithm to allow for the nonstationary effects are shown.

Conflicting evolutionary and biostratigraphical trends in Nephrolepidina praemarginata (Douvillé, 1908) (Foraminiferida)

Six late Rupelian populations of Nephrolepidina praemarginata (Douvillé, 1908) have been isolated from a succession of the Caltavuturo Formation (Madonie Mts, Sicily). A total of 25 embryonal parameters were obtained from oriented equatorial sections of megalospheric specimens; 8 indexes were derived from selected parameters and 9 indexes were considered for the neanic apparatus, out of which 2 are introduced here: N05 (number of annuli in a radius of 0.5 mm) and r5 (distance occupied by the first five annuli). The data show marked deviations from the expected trend of traditional biometric measures; this is interpreted as dependent on environmental factors. Previous studies on the succession evidenced an increase in basin depth; this can be inferred also from the biometric analysis of the inner characters of the allochthonous Nephrolepidina tests. Here, we explore the paleobiological potential of parameters linked to embryo size and wall thickness, and discuss how depth-dependent parameters may affect the interpretation of evolutionary trends and biostratigraphy in radial foraminifers.

Analysis and Mathematical Solutions for Consolidation of a Soil Layer with Depth-Dependent Parameters under Confined Compression

AbstractThis paper presents several analytical solutions for the consolidation analysis of a soil layer with fairly general laws of variation of permeability and compressibility for both a single-drained condition and a double-drained condition. The solution is described in detail. A normalized time, T, is suggested. The average degree of consolidation exhibiting very good normalized behavior is shown. It is also revealed that the excess pore-pressure distribution of a nonhomogeneous soil layer may be quite different from the conventional Terzaghi’s solution. For the double-drained condition, some symmetrical characteristics of the average degree of consolidation and excess pore pressure are proved. Special cases of constant permeability, constant compressibility, or constant coefficient of consolidation, in which the other parameter is depth dependent, are analyzed on the basis of general analytical solutions. Results are presented in figures and tables for practical applications.

Photophysics and rotational relaxation dynamics of cationic phenazinium dyes in anionic reverse micelles: Effect of methyl substitution

We present here, a detailed photophysical and rotational relaxation dynamical study of three structurally analogous cationic dyes, namely, phenosafranin (PSF), safranin-T (ST), and safranin-O (SO), carried out in well characterized, monodispersed biomimicking anionic reverse micellar nanocavities composed of sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/heptane with increasing water contents. The dyes belong to the phenazinium family and they differ in terms of methyl substitution on the planar phenazinium skeleton. The objective of the present study is to investigate the modification in the photophysical and dynamical behavior of the dyes with the change in the size of the water pool of the reverse micelle and thereby to explore the role of methyl substitution. Steady state and time resolved emission and anisotropy studies have been exploited for the purpose. The dyes are found to exhibit a marked decrease in the fluorescence anisotropy with increasing water/surfactant mole ratio (w), i.e., the water pool size in the reverse micellar core, implying that overall motional restriction experienced by the molecules are decreased with increasing hydration. Some of the depth dependent fluorescence parameters such as fluorescence maximum, fluorescence anisotropy (r) have been monitored for exploring the microenvironment around the probes in the reverse micelles. Fluorescence studies suggest that at low w values, the probes do not penetrate into the reverse micellar core; rather it binds at the interfacial region. Estimates of the micropolarity at the binding sites of the probe molecule have been determined as a function of w. Finally, dynamic studies reveal that both the lifetime and rotational relaxation time decrease with an increase in w for all the three probes, the extent of the decrease being more for PSF than ST and SO. This indicates a stronger binding of the reverse micelle with ST and SO compared to that with PSF which is rationalized in terms of an increase in the hydrophobicity of the former two dyes because of the methyl substitution on the phenazinium moiety.

New BODIPY lipid probes for fluorescence studies of membranes

Many fluorescent lipid probes tend to loop back to the membrane interface when attached to a lipid acyl chain rather than embedding deeply into the bilayer. To achieve maximum embedding of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore into the bilayer apolar region, a series of sn-2 acyl-labeled phosphatidylcholines was synthesized bearing 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene-8-yl (Me(4)-BODIPY-8) at the end of C(3)-, C(5)-, C(7)-, or C(9)-acyl. A strategy was used of symmetrically dispersing the methyl groups at BODIPY ring positions 1, 3, 5, and 7 to decrease fluorophore polarity. Iodide quenching of the phosphatidylcholine probes in bilayer vesicles confirmed that the Me(4)-BODIPY-8 fluorophore was embedded in the bilayer. Parallax analysis of Me(4)-BODIPY-8 fluorescence quenching by phosphatidylcholines containing iodide at different positions along the sn-2 acyl chain indicated that the penetration depth of Me(4)-BODIPY-8 into the bilayer was determined by the length of the linking acyl chain. Evaluation using monolayers showed minimal perturbation of <10 mol% probe in fluid-phase and cholesterol-enriched phosphatidylcholine. Spectral characterization in monolayers and bilayers confirmed the retention of many features of other BODIPY derivatives (i.e., absorption and emission wavelength maxima near 498 nm and approximately 506-515 nm) but also showed the absence of the 620-630 nm peak associated with BODIPY dimer fluorescence and the presence of a 570 nm emission shoulder at high Me(4)-BODIPY-8 surface concentrations. We conclude that the new probes should have versatile utility in membrane studies, especially when precise location of the reporter group is needed.

Calibration of a land-surface model using data from primary forest sites in Amazonia

A land-surface model (MOSES) was tested against observed fluxes of heat, water vapour and carbon dioxide for two primary forest sites near Manaus, Brazil. Flux data from one site (called C14) were used to calibrate the model, and data from the other site (called K34) were used to validate the calibrated model. Long-term fluxes of water vapour at C14 and K34 simulated by the uncalibrated model were good, whereas modelled net ecosystem exchange (NEE) was poor. The uncalibrated model persistently underpredicted canopy conductance (gc) from mid-morning to mid-afternoon due to saturation of the response to solar radiation at low light levels. This in turn caused a poor simulation of the diurnal cycles of water vapour and carbon fluxes. Calibration of the stomatal conductance/photosynthesis sub-model of MOSES improved the simulated diurnal cycle of gc and increased the diurnal maximum NEE, but at the expense of degrading long-term water vapour fluxes. Seasonality in observed canopy conductance due to soil moisture change was not captured by the model. Introducing realistic depth-dependent soil parameters decreased the amount of moisture available for transpiration at each depth and led to the model experiencing soil moisture limitation on canopy conductance during the dry season. However, this limitation had only a limited effect on the seasonality in modelled NEE.

An improved description of soil hydraulic and thermal properties of arctic peatland for use in a GCM

AbstractThe UK Meteorological Office Surface Exchange Scheme (MOSES), which is currently implemented within Version 3 of the Hadley Centre GCM, was tested for an arctic peatland site in northern Finland (Kevo). This implementation of MOSES incorporated a new depth‐dependent parameterization of the thermal and hydraulic properties of peat with parameter values derived from measurements reported in the literature. The effect of increasing the number of model soil layers from four to 13 shallower layers was also investigated. Driving data were used that were collected during June, when the peat was still frozen below about 80 mm, to September 1997.Best model performance was given by the 13‐layer, depth‐dependent parameter description for both surface heat fluxes and soil temperatures. The simulated heat fluxes compared well with measurements, but simulated surface temperatures were too high. In preliminary runs the simulated distribution of unfrozen water in the soil was also unrealistic. In particular the model was unable to predict the rapid transition to above‐freezing conditions that occurred throughout the soil profile about the second week in July. Adjusting a parameter (k) of the soil‐freezing curve, which for peat can be used as a fitting parameter, produced a big improvement in the soil temperature profiles. A more accurate simulation of the freezing and thawing behaviour of organic soils requires that the processes that are hidden in the modified value of k are explicitly represented. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Estimating transport parameters in an undisturbed soil column using time domain reflectometry and transfer function theory

Modelling solute transport in the unsaturated zone is a complex problem given the inherent soil heterogeneity. Using time domain reflectometry (TDR) as described in this paper can improve data quality to be used in predictive models. The TDR technique requires appropriate calibration if it is to be used for solute concentration measurements under constant and varying water content. Two ways of determining the parameters in the relationship between bulk soil electrical conductivity, σ a, soil solution electrical conductivity, σ w and volumetric water content, θ, were used. Among the two calibration methods tested here, the one which involved eluting the soil with several pore volumes of water of known electrical conductivity under transient flow conditions in an undisturbed soil column gave a linear σ w− σ a− θ relationship with depth dependent parameters. The other calibration method involved the use of disturbed soil under static conditions and resulted in a curvilinear σ w− σ a− θ relationship. The former calibration was subsequently used to determine solute concentrations in breakthrough experiments. Two solute transport experiments were carried out in the same undisturbed soil column; one for steady-state and one for transient flow condition. Parameters of the convective log normal transfer function (CLT) model were determined using time-integral-normalized resident concentrations. It was shown that the stochastic-convective approach described the experimental data well. Horizontal heterogeneity was more important during the transient experiment, where the topsoil was periodically ponded during a short period, than in the steady-state experiment, where unsaturated conditions were maintained throughout the experiment. This increased heterogeneity during transient flow was also reflected by the fact that preferential solute flow was only observed in the column's outlet under transient conditions.

Integrated assessment of soil chemical status. 1. Integration of existing models and derivation of a regional database for Switzerland

A regional soil acidification model was developed by integration and adaptation of existing models. The regional model consists of the dynamic multi-layer soil chemistry model SAFE, its steady-state version INITSAFE, the atmospheric deposition and nutrient uptake reconstruction model MAKEDEP, and a routine with empirical relations concerning depth-dependent parameters. A scheme for the extraction of input to the regional model from available information of different geographical detail also was developed. Basic data sources considered were: 1) national surveys such as the National Forest Inventory, covering site specific information, 2) available point measurements of parameter values, and 3) literature sources. Not all parameters were available on a regional scale with sufficient resolution. Input required for the model calculations therefore was derived from the available data sources by means of transfer algorithms including spatial interpolation. Interpolation was done allocating parameter values determined at reference sites to conventionally mapped entities such as geological units, soil type, and other kinds of geographical information. The exercise resulted in a data base of the required 68 site-specific parameter values covering climatic, deposition and land use parameters, as well as stand characteristics and soil properties.

Reconstruction of Depth-Dependent Parameter Profiles Based on Photothermal Measurements

Microstructural changes in a near-surface zone, as they appear at the hardening of steel, machining of ceramics, laser treatments or wear, occur together with modifications of their thermal properties. Therefore, the influences of such processes on the surface layer become detectable non-destructively by photothermal means. Today, the thickness determination of the affected zone via calibration curves is regarded as state of the art, whereas an increasing attention is focused on the numerical evaluation of the depth-dependent parameter profile, i.e. the material changes as a function of depth, mostly obtained by destructive tests, as yet. This paper presents the theoretical basics of a parameter profile reconstruction, based on photothermally measured data. It compares analytical solutions, derived directly from the thermal diffusion equation (TDE), with numerical approaches using the Finite Difference Method (FDM), both aiming at a quick and non-destructive control of near-edge affecting processes. Both models are applied to photothermal measurements, leading to calculated depth profiles of hardness in steel, which are compared with data, destructively obtained from the same samples using Vickers indentation techniques.

Comparison of three stream tube models predicting field-scale solute transport

Abstract. In this paper the relation between local- and field-scale solute transport parameters in an unsaturated soil profile is investigated. At two experimental sites, local-scale steady-state solute transport was measured in-situ using 120 horizontally installed TDR probes at 5 depths. Local-scale solute transport parameters determined from BTCs were used to predict field-scale solute transport using stochastic stream tube models (STM). Local-scale solute transport was described by two transport models: (1) the convection-dispersion transport model (CDE), and (2) the stochastic convective lognormat transfer model (CLT). The parameters of the CDE-model were found to be lognormally distributed, whereas the parameters of the CLT model were normally distributed. Local-scale solute transport heterogeneity within the measurement volume of a TDR-probe was an important factor causing field-scale solute dispersion. The study of the horizontal scale-dependency revealed that the variability in the solute transport parameters contributes more to the field-scale dispersion at deeper depths than at depths near the surface. Three STMs were used to upscale the local transport parameters: (i) the stochastic piston flow STM-I assuming local piston flow transport, (ii) the convective-dispersive STM-II assuming local CDE transport, and (iii) the stochastic convective lognormal STM-III assuming local CLT. The STM-I considerably underpredicted the field-scale solute dispersion indicating that local-scale dispersion processes, which are captured within the measurement volume of the TDR-probe, are important to predict field-scale solute transport. STM-II and STM-III both described the field-scale breakthrough curves (BTC) accurately if depth dependent parameters were used. In addition, a reasonable description of the horizontal variance of the local BTCs was found. STM-III was (more) superior to STM-II if only one set of parameters from one depth is used to predict the field-scale solute BTCs at several depths. This indicates that the local-scale solute transport process, as measured with TDR in this study, is in agreement with the CLT-hypothesis.

Application of an improved self-starter to geoacoustic inversion

The self-starter is improved using the operator of the split-step Pade solution. In addition to providing greater stability and being applicable closer to the source, the improved self-starter is an efficient forward model for geoacoustic inversion. It is necessary to solve only O(10) tridiagonal systems of equations to obtain the acoustic field on a vertical array located O(10) wavelengths from a source. This experimental configuration is effective for geoacoustic inverse problems involving unknown parameters deep in the ocean bottom. For problems involving depth-dependent acoustic parameters, the improved self-starter can be used to solve nonlinear inverse problems involving O(10) unknown sediment parameters in less than a minute on the current generation of workstations.

Ray-acoustic caustic formation and timing effects from ocean sound-speed relative curvature

Using deterministic ray-acoustic modeling of 1000-km propagation in the North Pacific, a depth-dependent parameter of ocean sound channels has been found to strongly influence geometrical ray propagation. This parameter is the sound speed times the second vertical derivative of sound speed divided by the square of the first derivative. Ray and wavefront timing and intensity can be influenced within realistic ocean sound channels by unpredictable wavefront triplications and caustics. These triplications are associated with large values of the parameter at ray turning points. The parameter, a relative curvature, behaves as a random variable because of ocean finestructure, causing the unpredictability. The relative curvature has a higher mean value near the sound-speed minimum for both an internal-wave model and actual data, so that this mechanism is a plausible explanation of poor multipath resolution and identifiability late in North Pacific pulse trains.