Seal Formation Research Articles

Wetting rate, sodicity, and soil texture effects on infiltration rate and runoff

Surface sealing is determined by aggregate disintegration and clay dispersion, which in turn depend on aggregate wetting rate, and soil sodicity and texture. We hypothesised that soil susceptibility to seal formation increases when the aggregate wetting rate (WR) is increased, and that the effect of WR depends on soil texture and soil sodicity. The objective of this study was to investigate the effects of WR on seal formation, by observing infiltration rate (IR) and runoff, in cultivated soils varying in clay content and exchangeable sodium percent (ESP). Effects of 3 wetting rates (2, 8, and 64 mm/h) on IR and runoff from 6 Israeli soils exposed to 60 mm of simulated rain of deionised water were studied in the laboratory. The soils ranged in clay from 8.8 to 68.3% and ESP levels from 0.9 to 20.4. Effects of WR on soil infiltration rate and runoff depended on soil texture and soil ESP. In soils with low clay content (8.8%), the effect of WR on seal formation was negligible, whereas effect of ESP was significant. Conversely, in clay soils (>52.1%), WR had a predominant effect on IR and runoff, while the effect of ESP was notable yet secondary to that of WR. The soils with intermediate clay content (22.5–40.2% clay) were the soils most susceptible to seal formation, with WR and ESP having moderate effects on seal formation. Effects of WR on aggregate disintegration and seal formation increased with increasing clay content and aggregate stability. Conversely, the role of ESP in determining sealing decreased with an increase in clay content and in WR.

Changes in penetration resistance of Ultisols from southern China as affected by shearing

Shear stresses and soil properties modified due to stress play an important role during formation of seals in a series of rainfall events and during tillage. The objectives of the study were to evaluate the effects of the penetrometer geometry on the penetration resistance as affected by shearing under different initial soil conditions and to use the information on soil strength to elucidate shearing process. Nine homogenous air-dried soils (<2 mm) were sprayed and stored so as to obtain equilibrium soil water contents. The moist soils were sheared by horizontal displacement of layers of soil particles/aggregates in between hands in one direction. The soil cores were prepared with comparable bulk density before the measurement of maximum penetration resistance ( P max) with a small flat tip and a cone tip penetrometers. At a wide range from 0.05 to 6.2 MPa, P max was linearly correlated between the small flat tip and the cone tip penetrometers. The conversion ratio was higher under the saturation condition irrespective of the shearing effect. The penetrometer with the small flat tip was more sensitive for the weak soils. Shearing generally increased P max in most cases, but it decreased P max for some sandy soils under both saturated and unsaturated conditions and for a clayey soil under the saturated condition. The soil consisting of swelling clay exerted a decrease in P max. Rearrangement and/or sliding of particles/aggregates and increase in soil suction during shearing were attributed to the increase in P max. Increase in porosity due to the aggregation during shearing was ascribed to the decrease in P max. In addition, it was shown that agricultural cultivation resulted in a reduction in soil strength.

Amplitude variations with offset of pressure‐seal reflections

Knowledge of pressure compartments is essential for identifying potential risks in advance of drilling and in understanding the mechanism of hydrocarbon trapping and migration. These compartments are bounded by pressure seals which, under certain conditions, can be detected and characterized with seismic reflection data. Use of prestack seismic data requires the analysis of reflections generated at the pressure seals, such as the top of a reservoir, rather than the properties of the rock volume. In this sense, amplitude variations with offset (AVO) techniques can be a good tool to obtain information from such pressure seals or pressure transition zones. In this work, I investigate the AVO response of compartment seals by analyzing the plane‐wave reflection coefficients as a function of pore pressure (above and below the seal), incidence angle, and seal thickness. For the case investigated in this work (Berea sandstone with high gas saturation), the AVO effects are important at low effective pressures, that is, when the pore pressure approaches the confining pressure. In shale‐free transition zones, the anomaly is, in general, negative, whereas in shale/sandstone sequences, the anomaly can be positive or negative depending on seal thickness and formation pressure. In terms of the four‐category classification for AVO crossplotting, the PP anomalies are mainly class IV and class I.

In-vitro investigation of blood embolization in cancer treatment using magnetorheological fluids

In a ‘simulated’ simple blood network made of silicone tubes, three magnetorheological fluids made of iron and iron-oxide particles are compared for embolizing fluid flow under an applied magnetic field. The sealing strength and seal formation time are measured as a function of particle concentration, magnetic property, carrier fluid, and flow rate. Future applications for cancer therapy are discussed.

Modeling the dynamics of soil seal formation: Analysis of the effect of soil and rainfall properties

The dynamic model of soil sealing developed by Assouline and Mualem [1997] is applied to study the effect of the main variables affecting seal formation, namely, the rainfall characteristics, the flow conditions, and the soil properties. The model is further extended to provide for the first time a quantitative estimation of the effect of the soil and water chemical properties on infiltration during soil surface sealing. The predicted effects of the chemical conditions on infiltration seem to be in agreement with experimental observations. Also, the model is used to explain the wide variability in seal thickness, found in the literature, in terms of the resolution of the method applied to measure the soil bulk density.

RAINFALL ENERGY EFFECTS ON RUNOFF AND INTERRILL EROSION IN EFFLUENT IRRIGATED SOILS

Seal formation at soil surfaces is significantly affected by raindrop kinetic energy (KE). Soil sealing enhances runoff and soil erosion. It has been hypothesized that in soils exposed to rain (i) runoff and interrill erosion levels in soils previously irrigated with effluents differ from those in soils previously irrigated with fresh water (FW), and (ii) that the difference in runoff and interrill erosion between the previously irrigated effluent and FW samples depends on rain KE. The effects offour droplet KE levels (3.6, 8.0, 12.4, and 15.9 kJ m -3 ) of distilled water (DW) on runoff and wash erosion of four smectitic soils that had been irrigated for many years with fresh water or effluents was studied with a drip-type rain simulator. The soils used were a loamy loess (Calcic Haploxeralf) from Be'er Sheva Valley, a dark brown sandy clay vertisol (Chromic Haploxerert) from the Pleshet Plains (vertisol HH), and two dark brown heavy clay vertisols (Chromic Haploxerert) from Zevulun Valley (vertisol Y) and Western Galilee (vertisol E), Israel. For all soils, total runoff and wash erosion values increased with the increase in rain KE. Total runoff levels were lower for the FW-irrigated samples than for the effluent-irrigated soils, except for the highest KE where no differences in runoff between the two types of soils was noted. Conversely, for each soil and each rain KE, wash erosion was higher in the effluent-irrigated samples than in the FW-irrigated ones. Total runoff was affected mainly by changes in rain KE at the lower to medium range of the KE studied. Thus, the effects of irrigation water quality (i.e., effluents vs. FW) on total runoff was pronounced mainly at the low-to-moderate rain KE range; at high rain KE, the effects of irrigation water quality on runoff were negligible. Wash erosion was affected mainly by changes in rain KE at the medium-to-high KE range studied. That wash erosion increased markedly at the high rain KE values, despite the negligible change in runoff level, suggested that for KE > 12.4 kJ m -3 , seal formation was completed, and the contribution of runoff in facilitating transport for the entrained material was secondary to the role of soil detachment in determining wash erosion. The dependence of wash erosion (through soil detachment) on rain KE was greater than its dependence on the quality of the irrigation water that the soil was exposed to in the past (FW vs. effluent).

Polyacrylamide, Sediments, and Interrupted Flow Effects on Rill Erosion and Intake Rate

The reduction in the intake rate (IR) during interrupted irrigation is difficult to predict. Sediments in irrigation water decrease the effect of interrupted irrigation on IR. Polyacrylamide (PAM) reduces rill erosion, but its effect on IR is controversial. The effects of water quality (tap water, tap water containing sediments, and 10 g m−3 PAM solution) and interrupted flow on IR and rill erosion in an Alfisol (Calcic Haploxeralf) and a Vertisol (Typic Chromoxerert) were studied using laboratory miniflumes. Rill erosion in both soils was eliminated by the PAM treatment in both continuous and interrupted flow. The PAM application reduced IR in the Alfisol and increased it in the Vertisol. In the Alfisol, interrupted flow reduced IR of the PAM solution by 37% compared with only 18% for tap water. In the Vertisol, interrupted flow reduced IR only slightly and the decrease was not affected by the polymer. When the water contained sediments, cumulative infiltration was reduced by 22% for the Vertisol and 59% for the Alfisol in comparison with tap water. These reductions were attributed to depositional seal formation. The IR of the Alfisol was more susceptible to depositional seal formation than the Vertisol. The presence of sediments in water was effective in reducing rill erosion. The effects of interrupted flow with PAM on reducing IR were explained by partial blocking of the conducting pores leading to greater suction and compaction of the soil surface. For sediment‐laden irrigation water, interrupted flow had no advantage over continuous flow in reducing IR because of depositional seal formation associated with the sediments in the water.

Improving Infiltration of Irrigated Mediterranean Soils with Polyacrylamide

The effects of continuous (1·0 mg/l) and concentrated (10 mg/l) irrigation water-added polyacrylamide (PAM) on infiltration of a highly erodible Mediterranean soil were studied using recirculating furrow infiltrometers. Polyacrylamide avoided the seal formation observed in the wetted surface of the control furrow and helped to maintain higher infiltration rates for both PAM treatments. Mean final cumulative infiltration for the continuous and concentrated PAM experiments increased by 20 and 14%, respectively, as the result of reduced seal formation and surface sealing. Steady-state furrow infiltration rates, evaluated with disc infiltrometers 15 h after irrigation and under soil water tensions of 40 and 100 mm, confirmed the infiltration benefit of PAM treatments. Unsaturated hydraulic conductivity calculated under the same tensions revealed that the PAM-treated furrows were about 95% more permeable than the control. Polyacrylamide application also increased average saturated conductivity by 168% because of more unblocked pores in the treated furrows. The ability of PAM to influence surface soil conditions and improve infiltration can greatly enhance management of irrigated Mediterranean soils by allowing longer irrigation and higher inflow rates. Application of 10 mg/l in the inflow only during the advance phase of the irrigation can reduce labour, and ensures that loss of PAM from furrow tail water is minimized and that quantities applied during the season are reduced.

Irrigation with Effluent Water Effects of Rainfall Energy on Soil Infiltration

Seal formation at soil surfaces is significantly affected by raindrop kinetic energy (KE). We hypothesized that the deterioration in seal permeability of soils irrigated with effluents, relative to that of soils irrigated with fresh water (FW), is affected by raindrop KE. The effects of four droplet KE levels (3.6, 8.0, 12.4, and 15.9 kJ m−3) on the infiltration parameters of four Israeli smectitic soils that had been irrigated with FW or effluents, were studied with a drip‐type rain simulator. At the lowest KE (3.6 kJ m−3), final infiltration rate (IR) values for the FW‐irrigated samples were in the range of 9 to 14 mm h−1 and were significantly higher than the corresponding values for the effluent‐irrigated samples, suggesting that seals were not fully developed at this low KE and that the irrigation water type played a major role in determining soil permeability. At high KE (15.9 kJ m−3), the differences between the final IRs of FW‐irrigated and effluent‐irrigated samples of a given soil were small (&lt;1.1 mm h−1), suggesting that at high KE, the effect of drop impact overshadowed the effects of water quality on the final IR. Rate of seal formation was faster in the effluent‐irrigated samples than in the FW‐irrigated ones, regardless of rain KE. The sensitivity of all four soils to the use of effluents was the greatest at a rain KE of 8 kJ m−3 At both lower and higher rain KE levels, the effect of effluents on the final IR, relative to that of FW, was less severe.

Axolemmal repair requires proteins that mediate synaptic vesicle fusion.

A damaged cell membrane is repaired by a seal that restricts entry or exit of molecules and ions to that of the level passing through an undamaged membrane. Seal formation requires elevation of intracellular Ca(2+) and, very likely, protein-mediated fusion of membranes. Ca(2+) also regulates the interaction between synaptotagmin (Syt) and syntaxin (Syx), which is thought to mediate fusion of synaptic vesicles with the axolemma, allowing transmitter release at synapses. To determine whether synaptic proteins have a role in sealing axolemmal damage, we injected squid and crayfish giant axons with an antibody that inhibits squid Syt from binding Ca(2+), or with another antibody that inhibits the Ca(2+)-dependent interaction of squid Syx with the Ca(2+)-binding domain of Syt. Axons injected with antibody to Syt did not seal, as assessed at axonal cut ends by the exclusion of extracellular hydrophilic fluorescent dye using confocal microscopy, and by the decay of extracellular injury current compared to levels measured in uninjured axons using a vibrating probe technique. In contrast, axons injected with either denatured antibody to Syt or preimmune IgG did seal. Similarly, axons injected with antibody to Syx did not seal, but did seal when injected with either denatured antibody to Syx or preimmune IgG. These results indicate an essential involvement of Syt and Syx in the repair (sealing) of severed axons. We suggest that vesicles, which accumulate and interact at the injury site, re-establish axolemmal continuity by Ca(2+)-induced fusions mediated by proteins such as those involved in neurotransmitter release.

A Hydro-Geomechanical View of Seal Formation and Failure in Overpressured Basins

The formation of seals, and the consequent retention of overpressure, is a common and expected event during normal basin evolution in active basins that have a significant mudrock succession. Seal failure, and the resultant limitation to fluid-pressure increase (valve action), is also an expected process. Hydro-geomechanical concepts, including poro-elasto-visco-plasticity (PEVP), and discontinuum models, allow the processes of seal formation and failure to be explained, and predict the state of stress in, and behaviour of, overpressured rocks. Importantly, properties that relate to porosity (such as permeability) can be integrated with this approach. These concepts provide a capability to undertake simulations that can serve as predictive tools. The fluid/rock interactions in a basin can be viewed as a self-organizing system, in the sense that overpressure and the undercompaction it permits retard the creation of accommodation space, and hence act as a negative feedback mechanism that slows the loading rate.

Patch-Clamp-Induced Perturbations of [Ca2+]i Activity in Somatotropes

Somatotropes and GC cells, a GH-producing cell line, exhibit [Ca²⁺]_i oscillations that result from rhythmic Ca²⁺ action potentials. Determination of this operating mode required simultaneous recording of both parameters by fura-2 imaging and patch-clamp techniques. In order to test whether patch recording induces artificial alteration of the [Ca²⁺]_i oscillatory pattern, we recorded separately or simultaneously [Ca²⁺]_i and membrane potential. In the absence of any other stimulation, seal formation in patch-clamp recording evoked by itself a 2.5- to 4-fold persistent increase in basal [Ca²⁺]_i, speeded up their frequency (from 0.03–0.17 to 0.4 Hz) and changed their pattern to a tonic mode. Patch-induced [Ca²⁺]_i increase was reproduced by mechanical contact between the pipette and the membrane. It was reduced by nifedipine, a blocker of L-type Ca²⁺ channels, as well as by removal of external Na⁺. It was fully blocked by external Ca²⁺ removal or gadolinium. All patch-clamp-induced perturbations were reversed by membrane hyperpolarization. We propose that patch-clamp recording evokes Ca²⁺ entry through L-type Ca²⁺ channels either directly, or indirectly via membrane depolarization. This shows that patch recordings in endocrine cells showing mechanosensitivity have to be interpreted with caution, and explains why long-lasting patch recordings are so difficult to obtain.

Microbial gum formation from the decomposition of cotton gin trash

This investigation evaluated production of extracellular polysaccharides (EPS) from the decomposition of cotton gin trash (CGT) in aerobic, anaerobic and continuous percolating environments. A further variation of pre-rinsing CGT was investigated in order to determine if the pollution potential from CGT could be minimized. Since previous investigations have used a colorimetric method for quantifying EPS that yields varying results when the constituent sugars are at different molar concentrations, a gravimetric method was used to quantify EPS production. The accumulation of uronides in the bound EPS suggests that the bound portion is critical in seal formation. The anaerobic environment showed an initial increase of EPS to 3 mg/g CGT and then maintained a constant level. The aerobic environment produced 9 mg of EPS/g CGT after 26 days with a continuing upward trend. The continuous percolating environment had concentrations similar to the aerobic environment and showed decreased hydraulic conductivity with increased EPS.

Inverted double-gap isolation chamber for high-resolution calcium fluorimetry in skeletal muscle fibers.

Here we describe an improved inverted double-grease-gap isolation chamber that allows the formation of grease seals of high mechanical stability and high electrical resistance. We also provide a detailed description of the procedure used to mount the muscle fibers onto the apparatus. The new chamber permits the electrophysiological study of muscle fibers using an inverted microscope and high-resolution objectives, thus complying with the requirements of modern fluorescence confocal detection methods. The simplicity and reliability of the mounting procedure make this chamber preferable over other gap isolation chambers currently used for simultaneous electrophysiological and optical studies of calcium release. Experimental results obtained from amphibian muscle fibers are presented to illustrate the performance of the chamber when using global fluorescence detection, confocal spot detection, and laser confocal scanning imaging.

Petroleum geochemistry in exploration and development: Part 2—Applications

Dry holes show that our exploration tools are not perfect. A trap containing petroleum is the end product of a sequence of events that involved deposition of a reservoir rock, seal formation, development of a trapping configuration, generation of petroleum, migration to the trap, and preservation of the trapped petroleum. Together, these form a “petroleum system.”

25] Simplified fast pressure-clamp technique for studying mechanically gated channels

A fundamental feature of the tight seal patch-clamp technique is the existence of a suction port in the patch pipette holder. This is critical for applying suction to the membrane patch to form a tight seal. This feature also enables, after seal formation, the application of pressure/ suction to stimulate the membrane patch mechanically. Initially, mouth-applied suction was used to obtain the seal and provide the stimulation. Although this is convenient, it lacks precision in terms of the magnitude and duration of the mechanical stimulus. This chapter describes a simpler but fast system known as “pressure clamps” and provides more details for its construction. The basic strategy of the pressure clamp is that the desired pressure applied to the patch pipette is achieved by a balancing of pressure and suction. Central to this balancing is the use of a proportional piezoelectric valve whose opening is proportional to the applied voltage. Through feedback control of this valve, the amount of pressurized N 2 allowed to enter a mixing chamber can be regulated to balance the constant outflow due a continual vacuum efflux and thus achieve the desired pressure.

Software-based correction of single compartment series resistance errors

Resistance across a patch pipette following seal formation and attainment of the whole cell recording configuration can introduce considerable and sometimes non-intuitive errors into voltage clamp recordings. These errors can be corrected actively on most commercially available amplifiers, although decisions during the experiment often must be made concerning the degree of correction to be employed, and the decision is essentially irreversible once the data is recorded. Amplifier-based corrections assume a single compartment, and thus any degree of compensation could be applied after data collection with a delay of only a single digitization interval. This report describes computer algorithms that correct capacitative filtering that results from pipette series resistance as well as the voltage error for current responses with either linear or non linear current–voltage curves. The algorithms are designed to operate on data that are recorded at a single holding potential rather than in response to voltage steps. The simplest algorithm for correction of responses with linear IV consists of about a dozen lines of C code and can easily be incorporated into data analysis programs, spreadsheets, and mathematical analysis packages. Code, sample programs, and spreadsheets that implement these algorithms are available from ftp.pharm.emory.edu.

Compaction, Aging, and Raindrop‐Impact Effects on Hydraulic Properties of Saline and Sodic Vertisols

AbstractVertisols markedly swell and disperse when wet because of the high percentage of montmorillonite in the soil. We hypothesized that soil bulk compaction, time since soil wetting (aging), and raindrop impact affect seal formation, soil permeability, and salt leaching of Vertisols. Vertisol (Typic Chromoxererts) samples with exchangeable Na percentages (ESP) of 0.4 and 11.8 were subjected to simulated rainfall of deionized (DW) and saline (SW) (electrical conductivity [EC] = 5 dSm‐1) waters with 0 and 18.1 J mm‐1 m‐2 impact energies. In a Vertisol without aging (0.5 h of prewetting) and under zero compaction, subjected to DW and SW rainfall, seal formation controls the soil permeability. Under DW rainfall, the final infiltration rates (FIR) of the sealed and unsealed Vertisol samples were 6 and &gt;44 mm h‐1 at ESP 0.4, and 5 and 17 mm h‐1, respectively. Four days of aging without compaction, followed by DW rainfall, increased the FIR of unsealed soil to 37 and to &gt;44 mm h‐1 at high and low ESP, respectively, and that of sealed soil to 12 and 14 mm h‐1 at high and low ESP, respectively. Subjecting wet soil to pressure up to 800 kg m‐2 decreased the unsealed Vertisol FIR under DW rainfall to 8.9 and 27 mm h‐1 at high and low ESP, respectively. Seal formation and bulk compaction had little effect on salt leaching in the low‐ESP soil. Under bulk compaction or seal formation, the high‐ESP soil leachate EC decreased from 10.7 to 9.0 dS m‐1 after 300 mm of DW rain.

Importance of surface sealing in the erosion of some soils from a mediterranean climate

Poor aggregate stability and high erodibility of soils found in Mediterranean climates are often due to low organic matter content. The low organic matter content is sometimes compensated for by iron oxides that stabilize soil structure. Low water stability of aggregates often determines the propensity for soils to form surface crusts and seals (wet crusts). Seals reduce soil infiltration rate and may increase erosion by increasing runoff. We conducted rainfall simulation experiments on 30 cm×30 cm plots inclined at 9% slope in which we measured soil splash and wash erosion, runoff and splash volume for seventeen California soils. The soils ranged in clay content from 8 to 36%, ESP from <1 to 56%, and organic carbon from 0.4 to 7.0%. Infiltration rate was used as a measure of seal formation. Soils that had 3.1 to 7.0% organic carbon and 2.4 to 10.7% CBD extractable iron plus aluminum did not form seals, infiltration rate remained high throughout the rainfall run, and neither runoff nor erosion occurred. Soils with <20% clay, <3% organic carbon, and <2.0% CBD extractable Fe+Al readily formed seals that reduced infiltration rate and total volume of water infiltrated and increased the volume of runoff water and mass of soil eroded. Initial soil water content was also important in determining crusting and subsequently the volume of runoff and amount of erosion. These data show that the formation of soil seals increases runoff and erosion through the early stages of seal development and that organic matter and iron oxides are critically important factors in determining soil surface stability and erodibility.

Synchronized Spontaneous Ca2+ Transients in Acute Anterior Pituitary Slices

We investigated the organization of spontaneous rises in cytosolic free Ca2+ concentration ([Ca2+]i) due to electrical activity in acute pituitary slices. Real time confocal imaging revealed that 73% of the cells generated fast peaking spontaneous [Ca2+]i transients. Strikingly, groups of apposing cells enhanced their [Ca2+]i in synchrony with a speed of coactivation >1,000 microm/s. Single-cell injection of Neurobiotin or Lucifer yellow labeled clusters of cells, which corresponded to coactive cells. Halothane, a gap junction blocker, markedly reduced the spread of tracers. Coupling between excitable cells was mainly homologous in nature, with a prevalence of growth hormone-containing cells. We conclude that spontaneously active endocrine cells are either single units or arranged in synchronized gap junction-coupled assemblies scattered throughout the anterior pituitary gland. Synchrony between spontaneously excitable cells may help shape the patterns of basal secretion.