Low Permeability Values Research Articles

Finite element modeling of slug tests in an aquifer with stratigraphical and structural heterogeneities

AbstractSlug interference tests using an array of multilevel active and monitoring wells permit enhanced aquifer characterization. Analyses of these field test data rely on numerical inverse models. In order to provide synthetic data sets and to have a better understanding of the flow mechanisms, we used a three‐dimensional finite element analysis (FEHM) to explore the effects of idealized, stratigraphical (strata) and structural (faults) heterogeneities with low permeability values on the transient head field that is associated with slug tests in an aquifer. Firstly, we tested our model on homogeneous aquifers and the effectiveness of our modeling strategies have been validated via the excellent agreement of our modeling results with those of the semi‐analytical model of Liu & Butler (1995). In our heterogeneity investigations, we embedded vertical and horizontal zones of lower permeability into a homogenous, isotropic, and confined aquifer to represent low‐permeability faults and strata respectively. A slugged interval is located at the center of the aquifer. Effects of strata thickness and permeability contrast as well as other effects associated with the offset of low‐permeability strata were explored. In particular, modeling results are represented by contour maps of peak travel time and maximum head perturbation of generated hydraulic pulses. Furthermore, various phenomena, such as real‐time matrix diffusion, intermittent matrix–fracture interactions, and faster pulse arrival through a longer flow trajectory, are concretely presented in the snapshots of head perturbations in the aquifer. Our finite element modeling provides useful information for understanding the behaviors of diffusive pressure propagation in an aquifer with stratigraphical and/or structural heterogeneities, and for designing hydraulic tomography to enhance aquifer characterization.

A Protection of the Environment Through the Prevention of Surface Cracking~!2008-06-21~!2008-10-21~!2009-01-06~!

One of the main objectives of the top asphalt layer is to provide a protective surface against water penetration and other harmful liquids such as chemicals. However, current construction equipments do not provide finished asphalt surfaces that meet this quality and therefore, allowing the intrusion of several liquids through the asphalt layers and deeper into the underlying soils. Subsequently, the result is often polluted soils and possibly seepage of the chemicals to rivers and underground water endangering the environment, plants, animals and ultimately humans. Results of recent research proved that current steel drum rollers induce surface cracks that provide path for surface water to intrude into the pavement layer. The development of a new compactor, asphalt multi-integrated roller (AMIR), produces asphalt layers with tight surface texture which demonstrate very low values of permeability when compared with similar asphalt compactor using current rollers. The results of field measurements of permeability on four asphalt sections compactor using AMIR and steel rollers showed that AMIR compacted surfaces will significantly improve the tightness of the surface and will reduce the permeability by a factor of up to 10 to 1, when compared with measured permeability on surfaces compacted using steel rollers. The results are used to discuss the role of better compaction in the protection of the environment and reduction of possible harmful pollution of water and soils.

Sulfonated polyether ether ketone composite membrane using tungstosilicic acid supported on silica–aluminium oxide for direct methanol fuel cell (DMFC)

New composite membranes were prepared using sulfonated polyether ether ketone (SPEEK) polymer and inorganic proton conducting fillers developed from tungstosilicic acids (SiWA) loaded on silica–aluminium oxide (SiO 2–Al 2O 3) composite. SiWA was fixed on stable structure (composite oxide) so that it became insoluble in water. The SPEEK polymers were characterized using H NMR and FTIR. XRD analysis was performed on the inorganic proton conducing fillers to reveal the existence of the interaction between SiWA and composite oxide. The membrane structural properties and surface morphologies were characterized with SEM and their performance were examined in terms of proton conductivity, water uptake and methanol permeability. It was found that the presence of inorganic proton conducting fillers led to both high water uptake and proton conductivity (maximum value 6.1 × 10 −2 S cm −1). Low methanol permeability values were recorded for the membranes which appeared as a very promising material to be used in DMFC.

Predicting Air Permeability in Porous Media with Variable Structure, Bulk Density, and Water Content

Air permeability in unstructured porous media can often be predicted directly from air‐filled porosity based on one or two measurements of air permeability at different air‐filled porosities using existing predictive models. In structured media and media that change their physical characteristics (bulk density, water content, organic matter content, etc.) with time, the relationship between air permeability and air‐filled porosity is often very complex and consequently models for predicting air permeability in such media are not yet well established. We developed a simple model concept for predicting air permeability in porous media with variable structure. Predictions are based on water content, air‐filled porosity, and dry bulk density and the model uses a very limited set of input data. The model is able to predict air permeability throughout the entire water content–bulk density domain. A set of four measurements of air permeability at different values of water content and dry bulk density is required as input. The model was tested against a set of air permeability data from six porous materials (a total of 236 measurements) representing a wide range of material types, organic matter contents, water contents, and dry bulk densities. Excellent agreement between measured and predicted air permeability values was found except at very low values of air permeability for some of the materials.

Multiscale ensemble filtering for reservoir engineering applications

Reservoir management requires periodic updates of the simulation models using the production data available over time. Traditionally, validation of reservoir models with production data is done using a history matching process. Uncertainties in the data, as well as in the model, lead to a nonunique history matching inverse problem. It has been shown that the ensemble Kalman filter (EnKF) is an adequate method for predicting the dynamics of the reservoir. The EnKF is a sequential Monte-Carlo approach that uses an ensemble of reservoir models. For realistic, large-scale applications, the ensemble size needs to be kept small due to computational inefficiency. Consequently, the error space is not well covered (poor cross-correlation matrix approximations) and the updated parameter field becomes scattered and loses important geological features (for example, the contact between high- and low-permeability values). The prior geological knowledge present in the initial time is not found anymore in the final updated parameter. We propose a new approach to overcome some of the EnKF limitations. This paper shows the specifications and results of the ensemble multiscale filter (EnMSF) for automatic history matching. EnMSF replaces, at each update time, the prior sample covariance with a multiscale tree. The global dependence is preserved via the parent–child relation in the tree (nodes at the adjacent scales). After constructing the tree, the Kalman update is performed The properties of the EnMSF are presented here with a 2D, two-phase (oil and water) small twin experiment, and the results are compared to the EnKF. The advantages of using EnMSF are localization in space and scale, adaptability to prior information, and efficiency in case many measurements are available. These advantages make the EnMSF a practical tool for many data assimilation problems

Geo‐environmental characteristics of modified and ordinary bentonitic soils exposed to MTBE

Methyl tertiary‐butyl ether (MTBE) is the most common oxygenated fuel additive used to increase the octane rating and enhance the combustion efficiency of gasoline. This product is characterized as a harmful compound by the US EPA and has been shown to be a health threatening contaminant for human beings. The most contingent route for MTBE to enter the environment is its leaking from underground storage tanks (USTs). To avoid soil and groundwater contaminations because of leaking of MTBE, we investigated the performance of both modified and ordinary bentonite clays as liner systems at USTs sites in this study. Modified bentonites are synthesized by changing the original metallic cations in the structure of bentonite particles, thus converting the bentonite from hydrophilic to organophilic nature. In this research both modified and ordinary bentonites were investigated to evaluate MTBE adsorption efficiencies. As permeability is a major parameter in measuring contaminants flow in soils, tests were conducted to measure the permeability characteristic of bentonites. X‐ray diffraction (XRD) analyses were also carried out to evaluate the adsorption of MTBE to bentonites. The results indicated that basal spacing of modified bentonite particles was increased from 28.64 to 42.32 Å, thus showing MTBE adsorption to the soil. In terms of permeability tests, modified bentonites showed much lower permeability values compared to ordinary bentonites (1.9 order of magnitude reduction) when exposed to MTBE. Modified clays are a viable option for use as liner system material at MTBE contaminated sites.

Permeability measurements of natural and experimental volcanic materials with a simple permeameter: Toward an understanding of magmatic degassing processes

Permeability measurement of quenched volcanic porous materials is an important approach to understand permeability development and degassing of vesicular silicic magmas. In this study, we developed a gas permeameter to measure permeability of natural samples and experimental products. The permeameter has broad measurement ranges of pressure difference (10 1–10 5 Pa) and gas-flow rate (10 − 9 –10 − 5 m 3/s). These ranges enable us to measure viscous permeability in the range of 10 − 17 –10 − 9 m 2 for 1 centimeter-scale samples, using the Forchheimer equation, which includes the inertial effect of gas flow permeating through the samples. In addition, we improved the procedure for performing permeability measurements of mm-sized products of decompression experiments. Although a previous study reported the first permeability data for vesicular silicic glass products of decompression experiments, we found an overestimation in their permeability data due to problems in sample preparation, especially for very low permeability samples. Our improved measurements give lower permeability values than those of Takeuchi et al. (2005)(Takeuchi, S., Nakashima, S., Tomiya, A., Shinohara, H., 2005. Experimental constraints on the low gas permeability of vesicular magma during decompression. Geophys. Res. Lett., 32, L10312 doi:10.1029/2005GL022491). We also evaluated the inertial effect on apparent permeability calculated using Darcy's law under the conditions of permeability measurement and magmatic degassing. The permeability measurements indicate that the apparent permeabilities of highly permeable samples (> 10 − 10 m 2 in viscous permeability) are affected considerably by the inertial effect under a high-pressure gradient (> 10 5 Pa/m) and reduced by more than 0.5 orders of magnitude from their viscous permeabilities. Also under magmatic conditions, the reduction of apparent permeability by more than 0.5–1.0 orders of magnitude may occur during the degassing of highly permeable magmas driven by a high-pressure gradient.

An investigation on the permeability of different wood furnish materials

Abstract In wood-based composite mats, mass and heat transfer are substantially influenced by their gas permeability. Thus, reliable permeability data are needed if one wants to model and simulate those processes taking place prior, during, and after hot-pressing operations of the mat. In this study, wood particles of surface and core layer type were obtained from two particleboard manufacturers, using impact mills and knife ring flakers, respectively. The permeability measurements were performed on the initial materials, as well as on subsets of it obtained by laboratory sieving. Additionally, medium density fibreboard (MDF) fibres from three species, namely pine (Pinus sylvestris), spruce (Picea abies) and rubberwood (Hevea Brasiliensis) were investigated. Cross-sectional and within-plane permeability was measured for densities from 250 to 1000 kg m-3. The permeability of the core particle materials was determined on solidified samples. On the other hand, the surface particles and MDF fibres were investigated by means of a rapid testing method on loose furnish materials (without solidification). MDF mats exhibited lower permeability values than particle mats at low densities, but values were found in the same order of magnitude for high densities. Mainly, the small particles determine the pore structure and permeability of particle mats. Thickness and in-plane size of particles affect the mat permeability, with the in-plane size becoming primarily effective at elevated densities. The permeability of MDF fibre mats depends more on the anatomy of the raw material than on its size distribution. We suggest, based on computer simulations, that only the within-plane permeability has a strong effect on gas pressure and temperature conditions during hot pressing. The cross-sectional permeability does not play an essential role in this regard.

Properties of treated papers and plastic film influencing ethyl ester transfer

Abstract The objective of this work was to compare and understand the aroma compound barrier property of two impregnated–supercalendered papers, with or without surface coating, and one plastic film (BOPP) in standard conditions of temperature (25 °C) and relative humidity gradient (50%) for foodstuff storage. For that purpose, solubility, diffusivity and permeability coefficients were determined for a homologous series of ethyl esters with a range of physico-chemical properties and vapor concentrations. Whatever the aroma compound and its vapor concentration, the non-coated paper was the more permeable; the coated paper and BOPP presenting close and lower permeability values. The transfer behavior was mainly controlled by aroma compound diffusivity related to packaging microstructure. Mutual affinity between aroma compound and packaging surface, determined experimentally or estimated, was related to their respective hydrophobicity. Conversely to papers which were treated to become more hydrophobic, BOPP was surface-treated to become more hydrophilic. In the conditions of the study, ethyl hexanoate sorption slightly increased BOPP crystallinity.

A fruit‐specific plasma membrane aquaporin subtype PIP1;1 is regulated during strawberry (Fragaria × ananassa) fruit ripening

Despite the advances in the physiology of fruit ripening, the role and contribution of water pathways are still barely considered. Our aim was therefore to characterize aquaporins, proteins that render the molecular basis for putative regulatory mechanisms in water transport. We focused our work on strawberry (Fragaria xananassa) fruit, a non-climacteric fruit of special interest because of its forced brief commercial shelf life. A full-length cDNA was isolated with high homology with plasma membrane (PM) intrinsic proteins (named FaPIP1;1), showing a profile with high expression in fruit, less in ovaries and no detection at all in other parts. Its cellular localization was confirmed at the PM. As reported in other plasma membrane intrinsic proteins subtype 1 (PIP1s), when expressing the protein in Xenopus leavis oocytes, FaPIP1;1 shows low water permeability values that only increased when it is coexpressed with a plasma membrane intrinsic protein subtype 2. Northern blotting using total RNA shows that its expression increases during fruit ripening. Moreover, functional characterization of isolated PM vesicles from red stage fruit unequivocally demonstrates the presence of active water channels, i.e. high water permeability values and a low Arrhenius activation energy, both evidences of water transport mediated by proteins. Interestingly, as many ripening-related strawberry genes, the expression pattern of FaPIP1;1 was also repressed by the presence of auxins. We therefore report a fruit specific PIP1 aquaporin with an accumulation pattern tightly associated to auxins and to the ripening process that might be responsible for increasing water permeability at the level of the PM in ripe fruit.

A Simple Hybrid Circuit for Direct Determination of Fluorescence Lifetimes

A new circuit for the measurement of fluorescence lifetime is described. The technology may be used in sensors which rely on fluorescence quenching in the presence of chemical species such as O2 or H+. Fluorescence is excited by pulses of light from an LED modulated with a square wave. The same square wave is used to gate the resulting luminescence signal from the fluorophore in order to eliminate non-specific luminescence detected during the LED pulse, and to extract the first harmonic of the resulting train of fluorescence decays. The first harmonic is then compared to the excitation signal using simple digital logic, resulting in a pulse width modulated signal. This signal has direct trigonometric relationships to the fluorescence lifetime and to the concentration of the quenching molecule. Evaluation of a prototype of this circuit was successful; the relationships between the sensor output and quenching concentration were as predicted by theory. Observed lifetimes of the fluorophore Ruthenium (4,7-diphenyl-1,10-phenanthroline)32+ immobilized in a sol-gel (~3 to 13 s) exceeded the lifetimes reported for the same fluorophore dissolved in liquid solvents, indicating a stabilizing effect of the sol-gel and comparatively low values of oxygen permeability in this material. Rate constants for emission and quenching of the fluorophore by oxygen in the sol-gel were determined to be 7.6 x 104 s-1 and 2.8 x 105 (atms)-1, respectively. The simplicity of the circuit design compared to alternative technologies is particularly compelling where rapid multiplexing to many parallel sensors is required.

How should permeability be measured in fine‐grained lithologies? Evidence from the chalk

AbstractTwo chalk data sets from the Central North Sea (UK/Norway and Denmark) with a similar lithological classification and porosity values (5–20%) have a difference in permeability of up to three orders of magnitude. The method of measuring permeability was different for the two data sets: samples from UK/Norway were measured by transient pulse decay (TPD), while the Danish samples were measured by routine core analysis. Petrological and petrophysical characterization of samples from the two data sets have revealed that all samples display a similar range of rock properties; the differences are not due to regional facies variations. It is likely that the low permeability values reported by TPD have more validity than routine core analyses in measuring lower porosity and permeability chalk (5–20% porosity, <0.01 mD). The fact that large sections of North Sea chalk potentially have much lower permeability than previously reported has widespread implications for petroleum migration and entrapment, and overpressure generation.

Nitrogen and helium permeation tests of SiC f/SiC composites

The permeance of inert gases (N 2 and He) through coated SiC based ceramic composites both in form of tubes and discs has been measured, in particular SiC–SiC f/SiC functionally graded material tubes made of SiC–SiC f with a SiC polycrystalline sealing coating and chemically vapour infiltrated (CVI) SiC f/SiC composite discs have been tested. The permeation tests have been aimed at verifying the effectiveness of coatings obtained by chemical vapour deposition (CVD) and used for closing the porosity of the composite materials and assuring their gas sealing. The measurements have been carried out at room temperature with operating pressure in the range 130–500 kPa. The SiC–SiC f/SiC functionally graded material has shown very low permeability values. The CVI SiC f/SiC composite tested has shown rather low permeance values, although the material is not gas tight: its reduced permeance was attributed to both the high fibre percentage and the dense SiC coating.

An investigation into polypyrrole-coated 316L stainless steel as a bipolar plate material for PEM fuel cells

Increasing attention is being paid to the use of metallic materials as a replacement for non-porous graphite in bipolar plates (BPs) for polymer exchange membrane (PEM) fuel cells. The ideal BP material should demonstrate high values of electrical conductivity, thermal conductivity, corrosion resistance and compressive strength and low values of gas permeability and density. Although metallic materials demonstrate many of those properties, their corrosion resistance can be inadequate, which in turn can lead to unacceptable values of contact resistivity. In this study, polypyrrole was polymerized onto 316L stainless steel using galvanostatic and cyclic voltammometric methods. A dense coating of polypyrrole could be formed on SS316L using both electrochemical methods. The coatings had different morphologies. For galvanostatic coatings, the particle size increases with increasing applied current. For cyclic voltammometric coatings, the particle size increases with increasing the cycle number. The potentiodynamic tests show that the corrosion current density is decreased by about one order of magnitude and polarization resistance is increased by about one order of magnitude by coating with polypyrrole. Optical microscopy showed that there is less intergranular corrosion after coating with polypyrrole. Therefore, these dense polypyrrole coatings much improved the corrosion resistance of SS316L and the coated materials could possibly be used in polymer exchange membrane fuel cells (PEMFCs) as a bipolar plate material.

A Parametric Study of Horizontal and Multilateral Wells in Coalbed-Methane Reservoirs

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 96018, "A Parametric Study on the Benefits of Drilling Horizontal and Multilateral Wells in Coalbed-Methane Reservoirs," by N. Maricic, SPE, Chevron Corp., and S.D. Mohaghegh, SPE, and E. Artun, SPE, West Virginia U., prepared for the 2005 SPE Annual Technical Conference and Exhibition, Dallas, 9–12 October. The full-length paper attempts to identify the most appropriate drilling pat-terns for coalbed-methane (CBM) reservoirs of different thickness and with different characteristics. The comparison yardstick for this study is net present value (NPV). In this way, drilling cost is accounted for when comparing different horizontal and multilateral configurations. Dual-lateral, trilateral, quadlateral, and fishbone configurations were compared. Total horizontal well length as well as spacing between laterals (SBL) was studied. Introduction CBM Background. Coal represents an unusual reservoir rock because of its highly complex reservoir characteristics. Unlike conventional sandstone reservoirs where gas is found in a free state within the pore structure of the rock, the methane gas is adsorbed onto the internal structure of the coal, which allows a significant amount of gas to be stored in the coal rock. A coal-seam system is a naturally fractured heterogeneous reservoir characterized by macropores (the fracture system, also known as the cleat system) and micropores (coal-matrix system). In general, the coal cleat system is orthogonal, with one direction cross-cutting. CBM production depends on fracture spacing and fracture interconnection. If the cleat system is not sufficiently developed, gas production can be very difficult. This occurs as a result of the low porosity and permeability values of the matrix, making it almost impossible for gas to move from the matrix into the fractures. At the beginning, the coal system is in equilibrium and typically, water must be produced continuously from coal seams to reduce the reservoir pressure and release the gas. Gas from the coal can be produced only after initial system dewatering and lowering the reservoir pressure. The dewatering process can take anywhere from a few days to several months and depends on CBM-well configuration. Generally, water production declines until the gas rate reaches the peak value. This "time-to-peak-gas" is a critical parameter because gas production begins declining soon after reaching the peak. Horizontal Wells. One of the main advantages of horizontal wells is that well direction, shape, and position can be controlled. With horizontal wells, an almost ideal well position can be determined and achieved with respect to principal permeability directions of the coal. Proper well positioning as well as borehole length drilled perpendicular to the main fracture system of the coal can contribute significantly to draining large areas.

Structure properties and pore dynamics in aggregate beds due to wetting–drying cycles

AbstractAggregate hierarchy and porosity changes in aggregate beds as a consequence of wetting–drying cycles were studied in two Andisols and one Mollisol from Chile, collected at two depths. Bulk density and indirect tensile strength were measured in aggregates of different sizes. Aggregate beds were prepared in cylinders with two size classes. Six wetting–drying cycles between 0 and –60 hPa were applied. Bulk density (Db) of soil matrix was controlled after each cycle, and the macroporosity was calculated. A repellency index was measured in one of the Andisols. In addition, also the air permeability was measured after the sixth cycle.It could be proofed, that the aggregate strength is an appropriate parameter to evaluate the aggregate hierarchy, and this parameter is also more sensitive than aggregate Db to discriminate between the effects of land‐use intensity. Aggregate strength is furthermore well correlated with changes in pore water pressure and can be applied to relate strength values with aggregate development level. Only if the predrying exceeds pF > 3.0, aggregate strength correlates with Db. The more pronounced is the land‐use, the higher is the increase of Db values for aggregate beds. The decrease of coarse porosity during wetting–drying cycles can be explained by mass differences between saturated and equilibrated water conditions that considers the water around aggregates and within the contact area. Nevertheless, the relation of relative macroporosity change, calculated by Pexped where Dagg is the Db measured by clod method, and the relative Db change, is useful to explain possible presence of coarse pores inside the aggregates. The newly formed porosity prevents the water repellency, but after six cycles of drying, the repellency index increased in the topsoil while we could detect a decrease in the subsoil samples (under defined conditions in the laboratory) which we assume to be caused by microbial activity. The approaching of aggregates by drying cycles generates in Andisols a reduced area to air fluxes, with low values of air permeability.

Modified poly(phenylene oxide) membranes for the separation of carbon dioxide from methane

Two types of poly(phenylene oxide) (PPO) membranes were prepared: one by chemical modification through sulfonation using chlorosulfonic acid and another by physical incorporation with a heteropolyacid (HPA), viz., phosphotungstic acid. These membranes were tested for the separation of CO 2/CH 4 mixtures. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction techniques were used to confirm the modified structure of PPO as well as to understand its interactions with gaseous molecules. Scanning electron microscopy (SEM) was used to investigate the membrane morphology. Thermal stability of the modified polymers was assessed by differential scanning calorimetry (DSC), while the tensile strength was measured to evaluate their mechanical stability. Both chemical and physical modifications did not adversely affect the thermally and mechanical stabilities. Experiments with pure CO 2 and CH 4 gases showed that CO 2 selectivity (27.2) for SPPO increased by a factor of 2.2, while the PPO–HPA membrane exhibited 1.7 times increase in selectivity with a reasonable permeability of 28.2 Barrer. An increase in flux was observed for the binary CO 2/CH 4 mixture permeation with an increasing feed concentration (5–40 mol%) of CO 2. An enhancement in feed pressure from 5 to 40 kg/cm 2 resulted in reduced CO 2 permeability and selectivity due to the competitive sorption of methane. Both the modified PPO membranes were found to be promising for enrichment of methane despite exhibiting lower permeability values than the pristine PPO membrane.

Stability of stratified elastico-viscous Walters' (Model B') fluid in the presence of horizontal magnetic field and rotation in porous medium

Combined effect of magnetic field and rotation is considered on the stability of stratified visco-elastic Walters' (Model B') fluid in porous medium. In contrast to the Newtonian fluids, the system is found to be unstable at stable stratification for low values of permeability or high values of kinematic viscoelasticity. Magnetic field is found to stabilize the small wavelength perturbations for unstable stratification. Variation of growth rate in the case of unstable stratification is depicted graphically with the variation in viscosity, viscoelasticity and permeability. It has been found that the growth rate increases with the increase in kinematic viscosity and permeability, whereas it decreases with the increase in kinematic viscoelasticity.

Transport and Bioavailability Studies of Astragaloside IV, an Active Ingredient in Radix Astragali

Astragaloside IV is an important constituent of Radix Astragali, a herbal remedy widely used in traditional Chinese medicine. Radix Astragali is administered orally but little is known about the transport properties and bioavailability of astragaloside IV. In this paper we report studies of the absorption of astragaloside IV in the perfused rat intestinal model, transport and uptake in Caco-2 cell monolayers and in vivo bioavailability in rat after an oral dose. In the perfused rat intestinal model, absorption of astragaloside IV was low from an aqueous solution but was significantly higher from a solution of Radix Astragali. Absorption was not affected by bile duct ligation. Transport through Caco-2 cells gave a very low permeability value (mean P(app) of 6.7+/-1.0 x 10(-8) cm/sec.) and uptake was unaffected by P-glycoprotein inhibitors. The absolute bioavailability of astragaloside IV in rat was 2.2%. The correlation between low permeability in vitro and poor bioavailability in vivo indicates in vitro absorption studies are useful in the evaluation of traditional Chinese medicines.

Distribution of the sheet current in a magnetically shielded superconducting filament

The distribution of the transport current in a superconducting filament aligned parallel to the flat surface of a semi-infinite bulk magnet is studied theoretically. An integral equation governing the current distribution in the Meissner state of the filament is derived and solved numerically for various filament–magnet distances and different relative permeabilities. This reveals that the current is depressed on the side of the filament adjacent to the surface of the magnet and enhanced on the averted side. Substantial current redistributions in the filament can already occur for low values of the relative permeability of the magnet, when the distance between the filament and the magnet is short, with evidence of saturation at moderately high values of this quantity, similar to the findings for magnetically shielded strips.