Wide Range Of Water Contents Research Articles

A multi-step inflow method for estimating hydraulic conductivity at low pressure under the wetting process

The accurate determination of the wetting soil hydraulic properties for a wide range of water contents is essential for studying and predicting infiltration processes. We present a laboratory infiltration method for determining hydraulic conductivity function, K( θ), in the low-to-medium water content range. An initially air-dry soil core is subjected to infiltration from the bottom where the pressure head, ψ bot, is controlled through a membrane. As soon as the wetting front arrives at the soil surface, the top 0.5-cm layer is sliced for measurement of the water content. The ψ bot is stepwise increased as the hydraulic equilibrium is nearly attained at each step. The wetting water retention function, ψ( θ), is determined by curve-fitting the equilibrium inflow data and from the independently measured data obtained from vapor equilibrium. The parameter in the K( θ) is estimated inversely using the cumulative inflow and water content of the sliced layer. This method is verified through comparisons with K( θ) obtained by the Boltzmann transform method. Although requiring an additional operation, the slicing procedure is found to be valuable in enhancing the reliability of the optimized parameter. A sensitivity analysis shows that water vapor movement would be negligible under our experimental conditions.

Plastic Limit, Liquid Limit and Undrained Shear Strength of Soil—Reappraisal

The concept that plasticity index of soils can be defined as a range of water contents producing a 100-fold variation in undrained shear strength has been experimentally verified with the help of a large number of tests on soils of diverse nature. This has led to the redefinition of the plastic limit as the water content at which undrained shear strength is around 170 kN/m2. Undrained shear strength of a soil at the liquid limit can be considered to be around 1.7 kN/m2. Accordingly, both the liquid limit and the plastic limit have been determined in the present work by a single consistent method, i.e., the Swedish fall cone method. The undrained shear strength-water content relationship has been found to be log-linear for a wide range of water contents beginning from lower than the plastic limit to higher than the liquid limit. This resulted in the formulation of an expression for predicting undrained shear strength of a remolded soil at any water content based solely on its liquid limit and plastic limit.

Simultaneous use of newly adopted simple sensors for continuous measurements of soil moisture and salinity

Methods available to measure salinity and moisture content in arid and semi-arid regions are limited because of the high salinities and very wide range of water contents (i.e. from saturation near the water table to air dry in the evaporation front). This paper is focused on the instrumentation employed in monitoring salt and moisture profiles in a column study which has wide applicability in salinity research. Experiments were conducted in a specially designed evaporation chamber which provided high evaporative demand as experienced in arid and semi-arid regions. Intensively instrumented soil columns with a constant shallow saline water table were used. Moisture content was measured by thermal conductivity and salinity by 4-electrode probe. In each case, instruments were manufactured specifically for the purpose in order to provide the desired degree of spatial resolution. Two soil types, sandy loam and clay loam, were used. Results indicated that thermal-conductivity probes measured water content over a wide range from saturation to 0.16 m3/m3 for clay loam and to 0.09 m3/m3 for sandy loam soil with great sensitivity (R2 > 0.95) and were unaffected by salt accumulation. The 4-electrode probes provided reliable measurements (R2 > 0.95) of the salinity of the soil solution for the range relevant to agricultural application. However, the accuracy of the probe decreased with the decreases in the water content after permanent wilting point.

Rheological properties of poly(2-hydroxyethyl methacrylate) (pHEMA) as a function of water content and deformation frequency.

Poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels have been used, or suggested for use, in a wide range of biomedical applications. In many of these applications, the mechanical properties of the gel are important for its proper functioning. These properties are influenced by a number of factors, including water content. In this study the storage and loss shear moduli were measured as a function of frequency for gels with water contents ranging from 22% to 48% at a temperature of 37 degrees C. At low frequencies and high water contents, deformation frequency had little effect. However, at higher frequencies and lower water contents, both moduli increased markedly with increasing frequency. This can be explained by the gels approaching a glass transition. The curves describing the behavior of each gel were combined to form a master curve, using a method analogous to the time-temperature superposition principle. This master curve can be used to predict the shear moduli for gels with a wide range of water contents and loading frequencies. For example, for a gel with a water content of 47.8% (as a percentage of the mass of gel), the curve provides shear moduli values over a frequency range of 10(-2)-10(4) Hz.

Laboratory Evaluation of a Commercial Dielectric Soil Water Sensor

Development of management strategies for efficient water utilization of crop production requires measurements of changes in soil water content on a dynamic basis. Many of the methods currently used for measuring these changes are destructive, slow, or relatively expensive for large-scale investigations. A commercially available, low-cost, nondestructive soil moisture sensor for measuring changes in soil volumetric water content (VWC) on the basis of changes in the dielectric constant of the soil water was evaluated under laboratory conditions for two soil series (Amarillo fine sandy loam [fine-loamy, mixed, superactive, thermic Aridic Paleustalfs] and Pullman clay loam [fine, mixed, thermic Torretic Paleustolls]) and a potting material across a wide range of water contents. Probes were placed in containers filled with deionized water and soil. Containers with Amarillo fine sandy loam were placed in a programmable temperature chamber and subjected to a series of changes in both temperature and VWC. Containers with Pullman soil and potting material were only subjected to changes in VWC at a constant temperature. Probe output at a constant temperature between air dry and a VWC of 0.25 m3 m−3 was linear for the Pullman soil and potting material and nonlinear for the Amarillo soil. When the Amarillo soil temperature varied between 15.9 and 39.1°C−1 at a constant VWC, probe output changed the equivalent of 0.10 m3 m−3 The temperature sensitivity was 0.5 mV °C−1 for air-dry and about 5 mV °C−1 for wet Amarillo soil. We conclude that probe output is soil specific and, given the nonlinear response to increasing water content on some soils and sensitivity to temperature, will require soil-specific calibration equations.

Effect of reduced air pressure on soil thermal conductivity over a wide range of water content and temperature

To clarify the role of air molecules in coupled heat and mass transfer in soil, we measured the thermal conductivity of three kinds of soil (Ando soil, Red Yellow soil, and Toyoura sand) under reduced air pressure over a wide range of water content and temperature (10–75°C). The thermal conductivity increased sharply under reduced air pressure above a critical water content of the soil, becoming several times larger than that under normal pressure (101 kPa). The maximum thermal conductivity for each soil was obtained below 75°C and was similar to the thermal conductivity of some metals such as Mn, Hg and stainless steel. When the soil was drier than its critical water content, the thermal conductivity did not increase under reduced air pressure. The hydraulic diffusivity at the critical water content for each soil was of the order of 10−8 m2 s−1. This suggests that the latent heat transfer is enhanced by the circulation of the condensed water. However, very little is known about the effect of circulating water on the latent heat transfer under reduced air pressure. To make this clear, the thermal conductivity would need to be measured in the steady state under reduced air pressure.

Analysis of polycyclic aromatic hydrocarbons in soil: minimizing sample pretreatment using automated Soxhlet with ethyl acetate as extraction solvent.

A simplified sample pretreatment method for industrially PAH-contaminated soils applying automated Soxhlet (Soxtherm) with ethyl acetate as extraction solvent is presented. Laborious pretreatment steps such as drying of samples, cleanup of crude extracts, and solvent exchange were allowed to be bypassed without notable performance impact. Moisture of the soil samples did not significantly influence recoveries of PAHs at a wide range of water content for the newly developed method. However, the opposite was true for the standard procedure using the more apolar 1:1 (v/v) n-hexane/acetone solvent mixture including postextraction treatments recommended by the U.S. EPA. Moreover, ethyl acetate crude extracts did not appreciably effect the chromatographic performance (HPLC-(3D)FLD), which was confirmed by a comparison of the purity of PAH spectra from both pretreatment methods. Up to 20% (v/v) in acetonitrile, ethyl acetate proved to be fully compatible with the mobile phase of the HPLC whereas the same concentration of n-hexane/acetone in acetonitrile resulted in significant retention time shifts. The newly developed pretreatment method was applied to three historically contaminated soils from different sources with extraction efficiencies not being significantly different compared to the standard procedure. Finally, the certified reference soil CRM 524 was subjected to the simplified procedure resulting in quantitative recoveries (>92%) for all PAHs analyzed.

The effect of clay morphology on water relaxation

The frequency dependence of the permittivity of water in calcium kaolinite (clay) is measured. It is shown that two mechanisms contribute to dipole relaxation of water. One refers to water in the free volume of pores in the clay. The other is associated with bound water covering the porous surface. Experimental data are treated in terms of a fractal model of the medium. The frequency dependence of the permittivity in a wide range of water content in the clay is accounted for theoretically.

Evaluation of a Model for Predicting Compressibility of Forest Soils

AbstractSoil compressibility is an important soil physical property in the prediction of compaction behavior. The compression index, C, as a measure of compressibility, was determined for a wide range of South African forest soils and compared with existing models that utilize clay content as the independent variable. These models were tested using a model performance technique that distinguished between systematic (bias) and nonsystematic (random) errors. The maximum compression index, Cmax, was adequately predicted for all soil orders in this study and possessed a relatively low systematic error. The average compression index, Cmod, which was calculated in this study as the average of C values across a wide range of water contents, was generally underpredicted and showed a slightly higher systematic error than with Cmax. It is concluded that the slightly better performance of the models in predicting Cmax was due to the models being developed on moist to wet soils (Ψp > −100 kPa) when compression is at a maximum. Since compaction can also occur under moist to dry conditions, our results indicate that modelling compaction behavior for soils that occur in regions with a pronounced dry season will require compression indices developed across a wider range of water contents than is currently the case.

Water diffusion in biological porous systems: a NMR approach

The spin-echo nuclear magnetic resonance (NMR) technique together with paramagnetic ion doping are used to study structural parameters of plant samples, such as restricted dimensions, and cell interconnection both through membranes and by cell contact by studying simultaneous restricted diffusion and intercellular water transfer via various pathways. Also, peculiarities of water diffusion on the surface of cell-wall cellulose are studied over a wide range of water content.

The dependence of the electrical conductivity measured by time domain reflectometry on the water content of a sand

We present paired measurements of the water content and electrical conductivity collected in a laboratory column packed with a homogeneous, clean sand over a wide range of water content and pore water electrical conductivity (EC) conditions. The EC was determined using the method of Nadler et al. [1991] from waveforms collected with two‐rod time domain reflectometry (TDR) probes with and without baluns and with three‐rod probes without baluns. Following Heimovaara et al. [1995], we calibrated the probes in saline solutions to account for the series resistance of the cable and connectors. The calibrated EC shows a nonlinear dependence on the water content that is well described by a simple power relationship [Archie, 1942]. Recognizing that calibration in saline solutions is impractical for some TDR probes, we demonstrate that the EC response can be calibrated directly using the results of drainage events, incorporating only a separate calibration of the cable resistance. None of the probe designs shows any clear advantage for EC measurement.

Extremely fluid behavior of hydrous peralkaline rhyolites

The viscosities of a series of water-bearing peralkaline rhyolitic melts have been experimentally determined. The dry melt compositions are composed of a series of additions of Na 2O to a metaluminous base composition. The melts, initially hydrated at high pressures and quenched isobarically, have been prepared by cutting and polishing, then reheating across the glass transition at 1 atm where they are annealed to a relaxed metastable state and then investigated dilatometrically using micropenetration methods. The measurements have been performed in the viscosity range of 10 8.5–10 11.5 Pa s which corresponds to temperatures in the range of 675–220°C for these compositions. Despite the relatively low viscosities of dry peralkaline melts in comparison with metaluminous melts of similar SiO 2 content, the viscosities of peralkaline rhyolitic melts also decrease strongly and non-linearly with the addition of water. The resulting viscosity–temperature relationships for water-bearing peralkaline rhyolitic melts are shifted to much lower temperatures such that glass transition temperatures for moderate cooling rates correspond to extraordinarily low temperatures. A model is presented for the calculation of melt viscosities in the range of 10 8.5–10 11.5 Pa s for peralkaline rhyolites with up to 7 wt% H 2O. The very fluid nature of these peralkaline rhyolites over a wide range of water contents may facilitate a very efficient degassing history of glassy peralkaline rhyolites in nature. Efficient degassing might explain the apparent contradiction of the presence of common water-rich melt inclusions in phenocryst phases hosted in water-free glassy rhyolites, versus the absence of vesicular layers or textural evidence for a vesicular past for the glassy rocks.

Investigations on the Influence of the Type of Extruder for Pelletization by Extrusion-Spheronization. II. Sphere Characteristics

Three different extruders, the Alexanderwerk gravity-feed roll extruder, the Gabler axial, single-screw extruder, and the NICA radial-screw extruder, were compared for their suitability for different placebo formulations and for fenoldopam pellets. A fourth extruder, the experimental ram extruder, was also included in some of the comparisons. The successful spheronization of extrudates from each of these extruders requires the correct water content. This water content, however, is different for each of the formulations and for each extruder. Generally, the Gabler unit required the highest amounts of water for a successful spheronization, yielding ⩾90% between 710 and 1250 um. The NICA unit needed much less water for the same formulation, and the Alexanderwerk unit required even less water than the NICA unit. Pellet sphericity was also strongly dependent on the correct water content of formulations, but was generally better for pellets produced with the Alexanderwerk or NICA units. A two-way ANOVA test for the individual formulations showed a significant difference in the mean particle size of batches produced with the NICA or the Alexanderwerk and the Gabler extruder. No significant differences could be found between any of the Alexanderwerk or NICA batches. Both extruders showed a linear dependence of the mean particle size on the water content of formulations, but the Gabler extruder showed an almost unchanged particle size over a wide range of water contents, provided that the formulation could be extruded successfully.Batches that were extruded on the NICA unit showed a significantly lower bulk density than comparable Alexanderwerk or Gabler batches. Comparing the true density of pellets, we found that significant differences could only be stated for Avicel PH 101 + water batches and only for the NICA/Gabler interaction. True density increased for all three extruders with increasing amounts of soluble components and with increasing water content. The NICA batches also exhibited a significant difference of the Hausner factor from the other two extruders, but no differences could be found in the friability of pellets.

Heat capacity and thermodynamic characteristics of denaturation and glass transition of hydrated and anhydrous proteins

Calorimetric measurements of absolute heat capacity have been performed for hydrated 11S-globulin (0 < C H 2O < 25%) and for lysozyme in a concentrated solution, both in the native and denatured states. The denaturation process is observed in hydrated and completely anhydrous proteins; it is accompanied by the appearance of heat capacity increment ( Δ N D C p), as is the case for protein solutions. It has been shown that, depending on the temperature and water content, the hydrated denatured proteins can be in a highly elastic or glassy states. Glass transition is also observed in hydrated native proteins. It is found that the denaturation increment Δ N D C p in native protein, like the increment ΔC p in denatured protein in glass transition at low water contents, is due to additional degrees of freedom of thermal motion in the protein globule. In contrast to the conventional notion, comparison of absolute C p values for hydrated denatured proteins with the C p values for denatured proteins in solution has indicated a dominant contribution of the globule thermal motion to the denaturation increment of protein heat capacity in solutions. The concentration dependence of denaturing heat absorption (temperature at its maximum, T D, and thermal effect, ΔQ D) and that of glass transition temperature, T g, for 11S-globulin have been studied in a wide range of water contents. General polymeric and specific protein features of these dependencies are discussed.

Methacrylate-capped fluoro side chain siloxanes: Synthesis, characterization, and their use in the design of oxygen-permeable hydrogels

Methacrylate end-capped 3-(2,2,3,3,-tetrafluoropropoxy)propyl, 3-(2,2,3,3,4,4,5,5-octafluoropentoxy)propyl, and 3-(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluorotridecoxy)propyl side chain siloxanes were evaluated for potential use in hydrogels for contact lens application. The preparation of the methacrylate end-capped perfluoro side chain siloxanes was accomplished in two relatively simple synthetic steps. The first step consisted of the acid-catalyzed co-ring opening polymerization of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and 1,3-bis-methacryloxybutyltetramethyldisiloxane, followed by a platinum-catalyzed hydrosilation with the tetrafluoro-, octafluoro-, and dodecafluoro-substituted allylic ethers. The incorporation of the terminal [—CF2—H] functionality had a dramatic effect on the increased solubility of the fluoro siloxane with hydrophilic monomers. Radical bulk polymerization of the methacrylate-capped fluoro side chain siloxanes with hydrophilic monomers, such as dimethylacrylamide and N-vinyl pyrrolidinone, resulted in transparent hydrogels possessing a wide range of water contents, high oxygen permeability, and a low modulus of elasticity. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1081–1089, 1997

Dielectric relaxation spectroscopy in poly(ethylene oxide)/water systems

AbstractThe dielectric properties of poly(ethylene oxide) (PEO) are studied by dielectric relaxation spectroscopy measurements in wide ranges of frequency (5–2×109 Hz) and temperature (193 − 300 K). PEO/water systems are also studied in a wide range of water content h (0 − 0.85 grams of water per grams of dry PEO). The measurements allow to distinguish between the dipolar secondary mechanism γ and effects related to free charge motion. The data are analyzed within the formalisms of permittivity, ϵ*, and electric modulus, M*. The water has been found to plasticize the dipolar process and to affect strongly the conduction process. A critical water content hc, hc = 0.13, has been found for the mechanism of charge transport.

1H NMR Measurements of Wet/Dry Ratio andT1,T2Distributions in Lung

Proton-magnetic-resonance measurements have been carried out on juvenile porcine peripheral lung parenchyma. The free-induction-decay signal contained a motionally restricted component which decayed in a few tens of microseconds and a mobile component with aT2time greater than 1 ms. The average second moment,M2, for the motionally restricted signal was found to be 3.42 ± (0.25) × 109s−2. TheT2distribution for the mobile signal consistently showed four resolvable components ofT2range: 2–6, 10–40, 80–110, and 190–400 ms. The 2–6 ms component was present in a fully dehydrated preparation and was therefore assigned to a nonaqueous lung constituent. The motionally restricted FID component had aT1= 0.772 ± 0.11 s and the mobile component had aT1= 0.967 ± 0.02 s. The hydrogen content per unit mass for lung parenchyma and water were estimated in two ways: (1) on the basis of chemical content and (2) on the basis of comparison of restricted and mobile signals to the gravimetric (G) water content for a lung sample studied at a wide range of water contents. Lung wet/dry weight ratios were estimated from the free-induction decays and compared with gravimetric measurement. The ratio of (wet/dry)NMR/(wet/dry)Gwas 1.00 ± 0.08 and 1.00 ± 0.05 for the two methods of estimation.

Rates of grain boundary diffusion through enstatite and forsterite reaction rims

The growth rates of enstatite rims produced by reaction of Fo92 and SiO2 were determined at 250–1500 MPa and 900–1100°C for a wide range of water contents. Growth rates were also determined for forsterite rims between MgO and Mg2Si2O6 and between MgO and SiO2. Rim growth rates are parabolic indicating diffusion-controlled growth of the polycrystalline rims which are composed of ˜ 2 μm diameter grains. Rim growth rates were used to calculate the product of the grain boundary diffusion coefficient (D'A) times the effective grain boundary thickness (δ) assuming in turn that MgO, SiO2, and Mg2Si−1 are the diffusing components (coupled diffusion of a cation and oxygen or interdiffusion of Mg and Si). The values for D'MgOδ, D'\(\), and D'\(\) for enstatite at 1000°C and 700 MPa confining pressure with about 0.1 wt % water are about five times larger than the corresponding D'Aδ values for samples initially vacuum dried at 250°C. Most of the increase in D'Aδ occurs with the first 0.1 wt % water. The activation energy for diffusion through the enstatite rims (1100–950°C) is 162 ± 30 kJ/mole. The diffusion rate through enstatite rims is essentially unchanged for confining pressures from 210–1400 MPa, but the nucleation rate is greatly reduced at low confining pressure (for ≤ 1.0 wt % water present) and limits the conditions at which rim growth can be measured. The corresponding values for D'Aδ through forsterite rims are essentially identical for the two forsterite-producing reactions when 0.1 wt % water is added and similar to the D'Aδ values for enstatite at the same conditions. The D'Aδ values for forsterite are ˜ 28 times larger for samples starting with 0.1 wt % water compared to samples that were first vacuum dried. Thus water enhances these grain boundary diffusion rates by a factor of 5–30 depending on the mineralogy, but the total range in D'Aδ is only slightly more than an order of magnitude for as wide a range of water contents as expected for most crustal conditions.

Spin-lattice relaxation behaviour of water in cellulose materials in relation to the tablet forming ability of microcrystalline cellulose particles

Medical tablet forming ability of microcrystalline cellulose (MCC) was investigated in relation to the mobility of water molecules in MCC particles. For this purpose, the spin-lattice relaxation time T1 of water in the system was measured by 1H-NMR. Over a wide range of water contents (0.02 ≤ H2O/cellulose (g/g) ≤ 1.79), two different T1 (T1,l and T1,s) values were observed for water in each MCC sample. Below the equilibrium water content, water having these two different T1 values exchange with each other in an MCC particle reaching an equilibrium state within a given time scale (equilibrium constant K). The T1,l, T1,s and K values for water in MCC, estimated at the equilibrium water content, showed fairly good correlations with the hardness of the tablets made by the MCC samples. Sample with a shorter T1, or larger K tended to have a stronger tablet forming ability. In the spin-spin relaxation time T2 measurements for protons in an MCC/D2O system, two T2 components originating from the glassy cellulose solid (T2,G) and the swelling region (T2,l) were observed. It was found that the mole fraction xL of protons with T2,L in the system exhibits a clear linear correlation with K. From these results, a structural model for the distribution of water in MCC particles was propoed by taking the surface of each microfibril and the disordered region within the microfibril into consideration

Holographic Sensor for Water in Solvents

The diffraction color of a gelatin holographic diffraction grating changed as a function of the water activity when immersed in a "wet" hydrophobic liquid. Quantification of the absorption maximum of the diffracted light showed that it was related, after calibration, to either the water content or the water activity of the solvent. The holographic diffraction grating measured water contents of hydrocarbon solvents at sensitivities comparable to that of the Karl Fischer coulometric titrator and over a wide range of water contents. A grating immersed in xylene revealed a visible color change when the water content was increased from 47 to 120 ppm. Conversely, the holographic grating responded to ethanol in water in the range 0-1% (w/w). The inexpensiveness and simplicity of silver halide holographic reflection gratings, combined with their relatively high sensitivity, suggests that these devices might find widespread application as immersible water activity sensors for hydrophobic liquids.