Saturated Conductivity Research Articles

Delineating Salinity and Sodicity Distribution in Major Soil Map Units of El Paso, Texas, Using Electromagnetic Induction Technique

A majority of the irrigated area in the Trans-Pecos basin in the United States is affected by both salinity and sodicity that affect the long-term viability of irrigated agriculture in the region. Accurate information on spatial distribution of salinity and sodicity in the irrigated areas at a field scale is necessary for developing effective management practices. Currently, information on the amount and the distribution of salts within the irrigated areas of the Trans-Pecos basin is not available. Conventional method of soil salinity (saturated paste electrical conductivity) and sodicity (sodium adsorption ratio) assessment at a high spatial resolution is expensive, time consuming, and labor intensive. Electromagnetic induction technique can offer a low-cost, noninvasive, and rapid alternative for determining the spatial distribution of both salinity and sodicity. In this study, we evaluated the accuracy of EMI technique to delineate salt and sodicity distribution within a 12-ha study site that had all four dominant soil map units (Saneli-clayey over sandy or sandy-skeletal, montmorillonitic [calcareous], thermic Vertic Torrifluvents; Tigua-very fine, montmorillonitic (calcareous), thermic Vertic Torrifluvents; Harkey-coarse-silty, mixed [calcareous], thermic Typic Torrifluvents; Glendale-fine-silty, mixed [calcareous], thermic Typic Torrifluvents) of the Trans-Pecos basin. Salinity and sodicity values estimated by EMI technique ranged from 0.73 to 10.55 dS m−1 and sodium adsorption ratio ranged from 1.2 to 21.6 mmol1/2 L−1/2. Results of this project indicated that the EMI technique can produce accurate information on salinity distribution. Soil clay and moisture content at the time of the survey strongly influenced the accuracy of the EMI technique.

Model for Power SiC Vertical JFET With Unified Description of Linear and Saturation Operating Regimes

A novel SiC junction field-effect transistor (JFET) model that uses a unified description of linear and saturated conduction modes is proposed. Advantages of the proposed model are improved robustness and convergence, inclusion of field-dependent mobility effects, and more physical description of the current saturation phenomenon. The model is validated against a normally off JFET sample over a wide temperature range. Finite-element simulations are used to demonstrate the physics-based nature of the proposed model.

Relative hydraulic conductivity in the vadose zone from magnetic resonance sounding — Brooks-Corey parameterization of the capillary fringe

The magnetic resonance sounding (MRS) method is used for noninvasive one-dimensional assessment of aquifer structures, i.e., for estimating the vertical water content and hydraulic conductivity distributions in the saturated zone. So far, MRS interpretation schemes for estimating the hydraulic conductivity as a function of the saturation degree in the vadose zone have not been developed. In this study we developed a new inversion scheme for MRS to estimate the relative hydraulic conductivity [Formula: see text], which is the ratio of the unsaturated and saturated conductivities. The new approach is based on the Brooks-Corey parameterization (BCP) of the capillary fringe; that is, the water content distribution of the capillary fringe is considered to be equivalent to the water retention curve in equilibrium state. The BCP inversion directly provides estimates of Brooks-Corey parameters from MRS data, which allows for the calculation of [Formula: see text] as a function of the saturation degree. In doing so, the water table must be given as a priori information for the MRS inversion. We tested the feasibility of this approach with a field example and its reliability and limitations with a set of synthetic models.

Pore-morphology-based simulations of drainage and wetting processes in porous media

Soil hydraulic properties relating saturation, water pressure, and hydraulic conductivity are known to exhibit hysteresis. In this paper, we focus on the determination of the water retention curve for a porous medium through a novel pore-scale simulation technique that is based on mathematical morphology. We develop an algorithm that allows for the representation of three-dimensional randomly packed porous media of any geometry (i.e. not restricted to idealized geometries such as spherical or ellipsoidal particles/pore space) so that the connectivity-, tortuosity-, and hysteresis-causing mechanisms are represented in both drainage and wetting processes, and their role in determining macroscopic fluid behavior is made explicit. Using this method, we present simulation results that demonstrate hysteretic behavior of wetting and non-wetting phases during both drainage and wetting cycles. A new method for computing interfacial surface areas is developed. The pore-morphology-based method is critically evaluated for accuracy, sample size effects, and resolution effects. It is found that the method computes interfacial areas more accurately than existing methods and allows for (i) examination of relationships between water pressure, saturation and interfacial area for hysteretic soils, and (ii) comparisons with previously developed theoretical models of soil hydraulic properties. The pore-morphology-based method shows promise for applications in vadose zone hydrology.

Observation of anomalous Hall effect in EuO epitaxial thin films grown by a pulse laser deposition

We have found that there is a narrow but distinct window in oxygen pressure for growing phase-pure epitaxial EuO films by a pulsed laser deposition. With finely decreasing the oxygen pressure, the electrical property is varied from insulating to metallic with an enhancement in Curie temperature from 70 to 120 K. The anomalous Hall contribution was clearly observed in Hall resistance at 5 K in the highest electron density sample. The saturated anomalous Hall conductivity (0.2 S/cm) is rather high in comparison with those of the other ferromagnetic oxides, probably due to strong spin-orbit coupling in EuO.

Relationship between hydraulic and basic properties for irrigated soils in southeast Australia

AbstractThis paper examines the potential of soil maps and spatial information on basic soil properties for predicting soil hydraulic properties in the Shepparton irrigation region (SE Australia). For this purpose, the relationship between locally measured soil hydraulic properties and basic soil properties, and soil categories was analyzed. Pedotransfer functions developed for Australian soil were tested. Furthermore, association of field‐scale final infiltration rates with basic soil properties was investigated. Water‐retention properties, and in particular subsoil water‐retention properties, were significantly correlated with readily available basic soil properties. Spearman's rank correlation coefficients were particularly high for clay content, bulk density, and the sum of exchangeable cations Ca2+, Mg2+, Na+, and K+. Water‐retention properties were adequately predicted using Australian pedotransfer functions. Water‐transmission properties such the saturated conductivity and the final infiltration rate were overall poorly correlated with basic physical and chemical properties. Generally, median water‐transmission properties did not significantly change with soil groups and “within‐paddock variability” accounted for over half of the “within‐soil‐type variability” for many soil types. We concluded that it is feasible to regionalize water‐retention properties for the Shepparton irrigation region using basic physical and chemical soil properties, whereas the information on basic soil properties and from soil maps was insufficient to reliably estimate water‐transmission properties. It is demonstrated why field‐scale estimates of final infiltration rates, obtained by fitting a model for surface irrigation to field measurements of advance, depletion, and recession, may be better correlated with basic soil properties.

Estimation of Saturated Paste Extracts’ Electrical Conductivity from 1:5 Soil/Water Suspension and Gypsum

Texture and salt type influence the relationships between saturated paste electrical conductivity (ECe) and EC of other soil/water ratios. The objectives of this study were to develop and validate relationships between ECe and EC1:5 suspension for soils in Yazd Province and evaluate the effects of soil texture and gypsum on those relationships. Three hundred twenty-two soil samples were collected, of which 272 (all data) were used to develop the models and 50 were used to validate them. The soils were divided into two general textural categories of coarse and fine and two categories of with (G) and without gypsum (NG). Gypsum content had a stronger impact on the accuracy of the suspension method in predicting ECe than texture. The ECe = 5.60 EC1:5 − 4.37 and ECe = 5.37 EC1:5 + 0.57 models are recommended for soils with and without gypsum, respectively. The methodology can be implemented in other regions, particularly if gypsum is present.

A Numerical Model of Transient Unsaturated Flow Under Centrifugation Based on Mass Balance

Numerical modeling of unsaturated flow in porous media under centrifugation is studied. A precise and numerically efficient approximation is presented for the mathematical model, based on Richards’ nonlinear and degenerate equation expressed in terms of effective saturation using the Van Genuchten–Mualem ansatz. The main difference with other methods is the utilization of a nonlocal condition based on mass balance. The method is suitable for determination of soil parameters, including the saturated conductivity, via the solution of an inverse problem in an iterative way. First, the fully saturated sample is centrifugated with a free outflow boundary during some time interval. Next, the output boundary is sealed and the sample is centrifugated for a prescribed time interval, or up to the creation of an equilibrium. Finally, the centrifugation is continued with a free outflow boundary. This procedure can be repeated to increase the information to drive the inverse problem. The application of the present method requires only non-intrusive, cheap measurements: rotational momentum and/or gravitational center of the sample, and optionally, the amount of expelled water.

Performance of a Mobile Salinity Monitoring Device Developed for Turfgrass Situations

Spatial salinity mapping with a mobile sensor platform allowing GPS‐labeled data on turfgrass areas would facilitate site‐specific leaching programs for salinity management. A salinity monitoring device (SMD) based on 4‐Wenner array electrical resistivity (ER) electrode configuration was developed for turfgrass sites and tested on three soils at Griffin, GA and a golf course fairway in Naples, FL on two dates where the fairway received saline irrigation water. Using directed soil sampling, the SMD resulted in soil apparent soil electrical conductivity (ECa) vs. laboratory saturated paste extract electrical conductivity (ECe) linear relationships with r2 of 0.59 to 0.87 (p < 0.0002) for 0 to 10 cm and 0 to 20 cm zones at Griffin, GA. For two mapping events varying two‐ to threefold in salinity levels at the golf course fairway, the ECa vs. ECe linear regressions exhibited similar slopes, different intercepts (due to two to threefold difference in background salinity), and r2 of 0.53 to 0.58 (p < 0.002). On another fairway, a detailed spatial salinity map using geographic information systems (GIS) methods was developed using a sampling grid of 2 by 3 m, which was well within the 19 m range determined for spatial autocorrelation of the data. Our data suggest the empirical methods developed for agricultural soils for relating ECa to ECe and for determining average ECa of discrete subsurface zones may differ under turfgrass conditions due to stratification of the surface organic matter layer influencing water holding capacity, soluble salt retention, and averaging ECa within a subsurface zone.

An Investigation of the Electrical Degradation of GaN High-Electron-Mobility Transistors by Numerical Simulations of DC Characteristics and Scattering Parameters

The effects of direct-current (DC) stress on GaN high-electron-mobility transistors (HEMTs) are investigated by means of numerical simulations, by which the creation of an acceptor trap in the AlGaN barrier layer was correlated to the observed experimental degradation. An increase in the trap concentration induces a worsening of the saturated current I DSS, transconductance g m, and output conductance g O. An increase in the length of the trapping region induces a degradation of I DSS and g m, but can reduce g O. Analysis of scattering parameters in the saturation region shows that the cutoff frequency f T matches the trend of g m.

Theoretical-experimental analyses of simple geometry saturated conductivities for a Newtonian fluid

The conductivity (K) of porous media represents an important physical parameter in several areas of knowledge. In saturated flow, the saturated conductivity (K0) is the most important parameter of porous system and it is related to the fluid and porous media properties. In order to evaluate the potential of a new tool for measuring K0, such as the computational simulation with Boltzmann models for fluid flows, two experiments were carried out using two simplified media: 1) a cylindrical cavity and 2) a cavity having a parallelepiped shape. Both have simple geometries that allow analytical K0 solutions in order to compare with the experimental and simulated results. Glycerin was used as infiltrate fluid due to its high viscosity that permits laminar flows and the use of Darcy's law to evaluate K0. The results demonstrate a good agreement among techniques (experimental, computational, and analytical) of K0 determination for cavities that present Reynolds number (Re) smaller than one.

Effect of Electromagnetic Shielding on Electron Beam-Cured Multi-Walled Carbon Nanotubes/Epoxy Composites

In this study, the electromagnetic interference shielding properties of multi-walled carbon nanotubes/epoxy composites were investigated in the frequency region from 1 approximately 8 GHz (L, S and C bands). Electromagnetic shielding samples were fabricated using an electron beam. The electromagnetic shielding properties of these absorber specimens were measured by a network analyzer (Agilent, 4901A), and their fracture behavior was analyzed by scanning electron microscopy. It was found that the saturation conductance depends on the fraction of the multi-walled carbon nanotubes in the composite, which affects the initial permittivity. These results show that the dielectric loss is a dominant factor in the L, S, and C bands, and the resonance frequency of the composite increased with the increasing fraction of multi-walled carbon nanotubes. Finally, the reflection loss was calculated from the permeability and permittivity of these composites. Composite with 10 wt% multi-walled carbon nanotubes and 1.5 mm thickness showed a reflection loss below -20 dB in the L, S, and C bands. Therefore, it is believed that thin multi-walled carbon nanotubes/epoxy composites may be good candidates for microwave absorption applications.

Simultaneous Monitoring of Water Saturation and Fluid Conductivity in Unconsolidated Sand Columns

Electrical conductivity can easily be measured, but interpretation is ambiguous since saturation, fluid conductivity, and material properties are interacting parameters. This study aims to indirectly obtain fluid conductivity evolution in time and space in column experiments by repetitively applying two independent non‐destructive multi‐level methods. Water saturation, is derived from the difference in x‐ray attenuation by dry, partially and fully saturated sand filled columns. Also, it is used to calculate fluid conductivity from the electrical conductivity in time intervals for each depth level in the column. The investigated columns show distinct patterns for water saturation, electrical conductivity, and calculated fluid conductivity for individual imbibition and drainage steps at distinct grain‐size distributions. During imbibition, the unsaturated capillary fringe head shows a very unusual increase in electrical conductivity gaining with each step of capillary rise. During the drainage cycle, the electrical conductivity peak broadens and moves downward. The calculated fluid conductivities are much higher than expected, but correspond well to conductivity and ion strength of the extracted fluids. The strong increase in electrical conductivity was attributed to the fast rising capillary head fluids, which quickly accumulated all available ions around the particles and moved upward. The slow water was depleted, and showed even a different ion distribution pattern due to slowly reacting minerals. Monitoring of fluid conductivity in time and space by non‐destructive methods provides access to enrichment–depletion processes in the critical zone, in the laboratory and in the field. This is essential for understanding the development of hardpans in natural and anthropogenic environments, causing eventually supergene economic enrichment of metals.

Role of vacancies in transport and magnetic properties of nickel ferrite thin films

Nickel ferrite thin films were synthesized by pulsed laser deposition. It was determined that the monotonic increase in saturation magnetization and the non-monotonic increase in electrical conductivity depend on the oxygen partial pressure during the growth of the thin films. A substantial reduction in magnetization was found which ranged between 0.4% and 40% of the bulk value as the oxygen partial pressure increased from 0.2 × 10−6 Torr to 500 mTorr during the deposition of the films. There was a three orders of magnitude increase in conductivity for the sample prepared under the most oxygen deficient environment (partial pressure of oxygen 0.2 × 10−6 Torr). These variations in saturation magnetization and conductivity are described within the framework of cation/oxygen vacancies in an inverse spinel nickel ferrite structure. The changes in the electronic structure due to the presence of the vacancies were investigated using x-ray photoelectron spectroscopy, which confirmed the formation of lower valent Ni for the samples prepared in an oxygen deficient atmosphere.

A method for the determination of the hydraulic properties of soil from MODIS surface temperature for use in land‐surface models

Soil hydraulic properties (SHPs) play an important role in land‐surface models, but their spatial distribution is poorly known, and it is not feasible to make field measurements of SHPs everywhere they are needed. In addition, the scale SHPs are measured on (10 cm) is substantially smaller than the scale at which land‐surface models are run (>1 km). As a result, land‐surface models need landscape hydraulic properties (LHPs), not SHPs. We present a method for identifying LHPs from MODIS surface temperatures. We calibrated LHPs in the Noah land‐surface model using MODIS surface temperatures in 2005 at 14 sites from the Atmospheric Radiation Measurement Program (ARM) using locally observed forcing data from 2005. We then used observed flux data during this same time period for model verification. Next, we determined LHPs from MODIS surface temperature at five sites using High Resolution Land Data Assimilation forcing data from 2002. We then used these LHPS to run Noah with 2005 ARM forcing data and compared the output to the same observed 2005 fluxes. Fitting LHPs to MODIS data decreases the error in modeled latent heat flux from 98 W/m2 to 67 W/m2. Fitting LHPs to these same latent heat flux measurements decreases the error to 50 W/m2. Therefore, two thirds of the parameter estimation improvement from calibration to in situ flux data can be achieved using remotely sensed surface temperature. These results are insensitive to errors in other parameters. For example, changing albedo by 0.1 changes the saturated conductivity (Ks) by 10% and the van Genuchten “m” parameter by 1%. However, changing minimum canopy resistance by 40 s/m produced a significant but mutually compensating change in both Ks and “m.”

Reply to comment by N. Shokri and D. Or on “A simple model for describing hydraulic conductivity in unsaturated porous media accounting for film and capillary flow”

Reply to comment by N. Shokri and D. Or on “A simple model for describing hydraulic conductivity in unsaturated porous media accounting for film and capillary flow”

Rainfall variability and hydrological and erosive response of an olive tree microcatchment under no‐tillage with a spontaneous grass cover in Spain

AbstractMost studies on runoff and soil loss from olive orchards were performed on plots, despite the fact that measurements that examine a range of erosive processes on different scales are essential to evaluate the suitability of the use and soil management of this type of land. The main environmental limitations of much of the land used for olive orchards in the Mediterranean are the steep slopes and the shallow soil depth – and this was the case in the study area. Soil erosion and runoff over two hydrological years (2005–2006 and 2006–2007) were monitored in an olive orchard microcatchment of 6·1 ha under no‐tillage with spontaneous grass in order to evaluate its hydrological and erosive behaviour. Moreover, soil parameters such as organic matter (%OM), bulk density (BD) and hydraulic saturated conductivity (Ks) were also examined in the microcatchment to describe management effects on hydrological balance and on erosive processes.In the study period, the results showed runoff coefficients of 6·0% in the first year and 0·9% in the second. The differences respond to the impact of two or three yearly maximum events which were decisive in the annual balances. On the event scale, although maximum rainfall intensity values had a big influence on peak flows and runoff, its importance on mean sediment concentrations and sediment discharges was difficult to interpret due to the likely control of grass cover on volume runoff and on soil protection. In the case of annual soil erosion, they were measured as 1·0 Mg ha−1 yr−1 and 0·3 Mg ha−1 yr−1. Both are lower than the tolerance values evaluated in Andalusia (Spain). These results support the implementation of no‐tillage with spontaneous grass cover for sloping land, although the reduced infiltration conditions determined by Ks in the first horizon suggest grass should be allowed to grow not only in spring but also in autumn. In addition, specific measurements to control gullies, which have formed in the terraced area in the catchment, should be included since it is expected that they could be the main sources of sediments. Copyright © 2010 John Wiley & Sons, Ltd.

Hydraulic Conductivity Function from Water Flow Similarity in Idealized‐ and Natural‐Structure Pores

Our objective was to develop and evaluate a simple, primarily physically based hydraulic conductivity model for natural‐structure soils. The proposed model of the hydraulic conductivity function, K(θ), is based on particle‐size distribution (PSD), flow in idealized capillary tubes of uniform diameter, and measured saturated hydraulic conductivity (Ks). We assume that hydraulic conductivity at a given saturation is actually saturated conductivity of pores that remain filled at that saturation, i.e., insignificant contribution from unfilled pores. The PSD data are used to generate pore‐size distribution using the Arya–Paris model, based on soil water characteristics. Pores are first treated as idealized, and flow for each domain is calculated using the Hagen–Poiseuille flow equation. We further assume that the ratio of flow in any pore domain to total flow at saturation for idealized pores applies equally to natural‐structure pores. Using this equality, the total flow at saturation, obtained from measured Ks, is distributed among the natural pore domains. This approach is advantageous in that flow parameters remain constant for all soils. Using the model, we calculated K(θ) for 29 soils with a wide range of physical properties. Agreement between predicted and experimental data was excellent to good for 21 soils (r2 > 0.9 for 14 soils, >0.8 for 7 soils). Poorer agreement in the remaining soils was attributed to uncertainty in input and experimental K(θ) data. A 1:1 comparison of log‐transformed predicted and experimental data for the 29 soils (719 data pairs) showed significant scatter(r2 = 0.735, RMSE = 1.04), which is consistent with similar comparisons in the literature.

Elastomer foam nanocomposites for electromagnetic dissipation and shielding applications

A novel elastomer foamed nanocomposite has been developed with high electromagnetic dissipation and shielding properties. This light weight foamed fluorocarbon incorporates multi-walled carbon nanotubes at low loading concentrations to achieve levels of conductivity and energy shielding that surpass the requirements for electromagnetic static discharge (ESD) and electromagnetic interference (EMI) shielding. Foaming the elastomer reduces that weight by 30% with minimal impact on ESD or EMI characteristics. The percolation threshold is at about 2% carbon nanotubes and the saturation conductivity occurs at 8% carbon nanotubes by weight. Combining the good electrical properties with the flexibility and fluid resistance of fluorocarbon yields a very versatile yet light weight material for a variety of ESD and EMI applications.

Numerical Implementation of Streaming Down the Gradient: Application to Fluid Modeling of Cosmic Rays and Saturated Conduction

The equation governing the streaming of a quantity down its gradient superficially looks similar to the simple constant velocity advection equation. In fact, it is the same as an advection equation if there are no local extrema in the computational domain or at the boundary. However, in general when there are local extrema in the computational domain, it is a nontrivial nonlinear equation. The standard upwind time evolution with a CFL-limited timestep results in spurious oscillations at the grid scale. These oscillations, which originate at the extrema, propagate throughout the computational domain and are undamped even at late times. These oscillations arise because of unphysically large fluxes leaving (entering) the maxima (minima) with the standard CFL-limited explicit methods. Regularization of the equation shows that it is diffusive at the extrema; because of this, an explicit method for the regularized equation with $\Delta t\propto\Delta x^2$ behaves fine. We show that the implicit methods show stable and converging results with $\Delta t\propto\Delta x$; however, surprisingly, even implicit methods are not stable with large enough timesteps. In addition to these subtleties in the numerical implementation, the solutions to the streaming equation are quite novel: nondifferentiable solutions emerge from initially smooth profiles; the solutions show transport over large length scales, e.g., in form of tails. The fluid model for cosmic rays interacting with a thermal plasma (valid at space scales much larger than the cosmic ray Larmor radius) and the equation of saturated conduction in a collisionless plasma are similar to the streaming equation, so our method will find applications in fluid modeling of important processes in plasma astrophysics.