Coupled Transport Processes Research Articles

Étude par spectroscopie d'admittance et MEB de la dégradation électrique des couches minces de CuAlS2non dopé déposées sous vide

We have accelerated the ageing of CuAlS2 by the application of a static electrical field for different degradation times. We have investigated the admittance spectroscopy and the scanning electron microscopy to follow and understand the (mass-charge) coupled transport processes produced in the volume and on the surface of these films. The electrical constraint induces, after an incubation phase, an activated decrease of the resistance, followed by a susbstantial increase correlated to the formation of an open circuit. This degradation occurs more rapidly for the films having initially a lower resistance, due to the thermal dissipation which increases considerably the temperature to about 140 °C. Admittance spectra reveal, at low frequencies, a capacitive loop related to the formation of a charge space induced by copper diffusion. Such migration develop induces the formation of copper arborescences, spreading from the cathode towards the anode. The effect of these structures on the properties of the degraded films is discussed in relation to electromigration and associated processes (whiskers, fracture, healing, bridge-building, ...). Also, we have noticed their similarity with fractal phenomena such as electrodeposition and dielectric breakdown.

Current Problems of Heat and Mass Transfer in the Cryopreservation of Biomaterials: Interactions among Coupled Multiscale Transport Processes

Current Problems of Heat and Mass Transfer in the Cryopreservation of Biomaterials: Interactions among Coupled Multiscale Transport Processes

Na+-DependentL-Arginine Transport in the Pigmented Rabbit Conjunctiva

The objective of this study was to characterize Na+-coupledL-arginine (L-Arg) transport in the pigmented rabbit conjunctiva. The excised pigmented rabbit conjunctiva was mounted in the modified Ussing chamber for measurement of short-circuit current (Isc),3H-L-arginine (3H-L-Arg) flux, and22Na flux.L-Arg when added to the mucosal side led to 0.32–2.65 μA cm−2increases in the Isc at 37°C, but not at 4°C or in a Na+-free solution.L-Arg at 1 mMstimulated net Na+absorption by 0.12 μEq cm−2h−1. The evidence for carrier-mediated transport ofL-Arg includes: (1) temperature dependence and saturability over 0.01–10 mM, (2) Na+dependence and ouabain sensitivity, (3) 84±2% reduction in the apparent permeability coefficient (Papp) of3H-L-Arg in the presence of excess unlabeledL-Arg (1 mM), and (4) 16-fold difference inL-Arg transport (at 0.1 mM) between the mucosal-to-serosal and the serosal-to-mucosal direction. Moreover,L-Arg transport was inhibited by basic amino acids, large neutral amino acids, and nitric oxide synthase inhibitors, but not by acidic and small neutral amino acids. Kinetic analysis revealed the possible existence of both high and low affinity processes forL-Arg transport. A half maximal concentration (Km) and maximalL-Arg flux (Jmax) values of the low and high affinity processes were 5.90 and 0.07 mM, and 1,248 and 111 pmol cm−2min−1, respectively. Hill analysis ofL-Arg transport at 0.1 mMin the presence of varying Na+concentrations in the mucosal bathing fluid yielded a Hill coefficient of 0.93, suggesting a 1:1 coupling between Na+andL-Arg. In conclusion, Na+-coupled transport process(es) forL-Arg in accordance with a 1:1 stoichiometry appear to be present on the mucosal side of the pigmented rabbit conjunctiva. The pattern of inhibition by basic and large neutral amino acids and Na+dependency are suggestive of system B0,+-mediatedL-Arg transport.

Numerical Modeling of Coupled Electrochemical and Transport Processes in Lead‐Acid Batteries

A numerical model is developed to predict transient behaviors of electric vehicle lead‐acid batteries during discharge and charge processes. The model not only accounts for coupled processes of electrochemical kinetics and mass transport occurring in a battery cell, but also considers free convection resulting from density variations due to acid stratification. A single set of conservation equations valid for both porous electrodes and the free electrolyte region is derived and numerically solved using a computational fluid dynamics technique. This numerical methodology is capable of simulating a two‐dimensional cell with the fluid flow taken into consideration and requires only tens of minutes of central processing unit time on engineering workstations. Four sample calculations are presented in this work to provide rigorous validation of the developed simulator. The simulator is capable of predicting the transient behavior of the acid concentration, the porosity of the electrodes, and the state of charge of the battery during discharge, rest, and charge cycles. The model can also be used to investigate the effects of various system parameters, such as electrode dimensions, separator design, temperature, and electrolyte composition on the battery performance (voltage, power, cold cranking amperage, etc.).

Uncoupling of Adaptive Fading Kalman Observer Applied To Coupled Transport System

An adaptive fading Kalman observer (AFK) is applied to estimate temperatures along a counter-current heat exchanger. The gain is computed from Riccati equations using an adaptive forgetting factor. The analysis of this gain shows that the estimation error of the tvvo fluids could be decorrelated. Therefore correction could be decoupled even if the model equations are coupled. This result leads to the construction of uncoupling adaptive fading Kalman observer (UAFK). The possible extension of UAFK observer to other coupled transport processes is proposed.

Ca2+ transport processes of lobster hepatopancreatic brush-border membrane vesicles

45Ca2+ uptake by hepatopancreatic brush-border membrane vesicles of Atlantic lobster (Homarus americanus) occurred by a combination of three independent processes: (1) an amiloride-sensitive carrier-mediated transport system; (2) an amiloride-insensitive carrier-mediated transport system; and (3) a verapamil-inhibited channel process responsive to transmembrane potential. Both carrier-mediated processes were antiporters and capable of exchanging external Ca2+ with intravesicular Na+ or H+. The kinetic parameters of both carrier-mediated processes have been reported previously. External amiloride and Zn2+ were both competitive inhibitors of 45Ca2+ influx, reducing entry of the divalent cation at a single binding site with Ki values of 370 µmol l-1 for amiloride and 940 µmol l-1 for Zn2+. It is concluded that the mechanisms controlling Ca2+ entry into hepatopancreatic epithelial cells include a previously reported electrogenic 2Na+/1H+ antiporter, an electroneutral 2Na+/1Ca2+ antiporter and a verapamil-sensitive Ca2+ channel, which might also be used for the entry of Zn2+ and possibly other heavy metals. Evidence from an equilibrium-shift experiment, based on the thermodynamics of a coupled transport process, suggested that both monovalent (Na+) and divalent (Ca2+ and Zn2+) cations may enter hepatopancreatic epithelial cells through a common carrier-mediated transport protein. This suite of hepatopancreatic brush-border Ca2+ transport processes qualitatively resembles that previously reported for the luminal membrane of lobster antennal glands and suggests that crustacean epithelial cells from different organs may handle this divalent cation by similar means.

The Dissipated Energy of Electrode Surfaces: Temperature Jumps from Coupled Transport Processes

Nonequilibrium thermodynamics for surfaces has been applied to the electrode surfaces of an electrochemical cell. It is shown that the temperature of the surface differs from that of the adjacent electrolyte and electrode, and that a temperature jump exists across the surface. Mathematical expressions are derived for the temperature profiles of two cells at steady‐state conditions. Methods for estimating transport coefficients for the coupled transport processes at the electrode surface are discussed. Possible numerical results for the temperature profile, the overpotential, and the dissipated energy are reported. The results reflect the relative importance of heat conductivities, electric conductivities, and the Peltier coefficients for the electrode surface phenomena in combination with bulk properties. Significant temperature jumps may occur at normal electrolysis conditions 103 to , and for temperature jump coefficients which are smaller than . The overpotential may have contributions from the Peltier coefficients for the surface larger than the ohmic contribution. The method of analysis gives new information useful for heat control of electrochemical cells, electrode kinetic studies, and interpretation of overpotentials.

Abatement of acidification in mining lakes in Germany

AbstractOpen‐cast lignite mining has exposed formerly anaerobic layers to the air. Pyrite and marcasite are oxidized to sulfuric acid and iron sulfate, which later hydrolyses to iron hydroxide. When the pit is refilled with groundwater, its pH is 2–3. These geogenically acidified mining lakes are brown, with high iron content. Biological conditions differ greatly from those in most natural lakes and resemble those in sulfur‐acidic lakes impaired by acid rain. The usability of these fish‐free lakes is also restricted for recreational purposes.Neutralization with lime is expensive. The iron‐buffered water has a high base buffering capacity stabilizing at pH 2–4. The complex of potential measures for neutralization comprises: the revegetation of the waste heaps, the hydrological regime and coupled transport processes, the selection of suitable filling water and in‐lake technologies. Desulfurication takes place with sulfidic binding of iron and natural neutralization under locally anaerobic conditions in the reclaimed overburden heaps, in the deep water of mining lakes, in macrophyte stands and in the sediments.Anaerobic conditions should be established within the lakes during stratification periods: in the hypolimnion of eutrophic or the monimolimnion of meromictic lakes. Acidic lakes often are not sufficiently productive to achieve deep‐water oxygen depletion. Measures to increase the stability of stratification may be necessary, for example by installation of barriers to establish an environment suitable for biological neutralization. Carbon sources for microbial desulfurication may be added artificially or autochthonically produced by primary producers. Therefore, a controlled eutrophication may be useful in the initial filling stages of acidic mining lakes.

Basin‐scale hydrogeologic modeling

Mathematical modeling of coupled groundwater flow, heat transfer, and chemical mass transport at the sedimentary basin scale has been increasingly used by Earth scientists studying a wide range of geologic processes including the formation of excess pore pressures, infiltration‐driven metamorphism, heat flow anomalies, nuclear waste isolation, hydrothermal ore genesis, sediment diagenesis, basin tectonics, and petroleum generation and migration. These models have provided important insights into the rates and pathways of groundwater migration through basins, the relative importance of different driving mechanisms for fluid flow, and the nature of coupling between the hydraulic, thermal, chemical, and stress regimes. The mathematical descriptions of basin transport processes, the analytical and numerical solution methods employed, and the application of modeling to sedimentary basins around the world are the subject of this review paper. The special considerations made to represent coupled transport processes at the basin scale are emphasized. Future modeling efforts will probably utilize three‐dimensional descriptions of transport processes, incorporate greater information regarding natural geological heterogeneity, further explore coupled processes, and involve greater field applications.

Thermodynamic and Stochastic Theory of Coupled Transport Processes: Rayleigh Scattering in a Fluid in a Temperature Gradient

Thermodynamic and Stochastic Theory of Coupled Transport Processes: Rayleigh Scattering in a Fluid in a Temperature Gradient

Solute Transport Through an Integrated Heterogeneous Soil‐Groundwater System

The coupled transport process through an integrated soil‐groundwater system is quantified for kinetically sorbing solute that originates from a time dependent source at the soil surface and is transported by steady random velocity. The derived expressions of ensemble mean solute breakthrough at some arbitrary control plane normal to the mean flow direction involve probability density functions (pdfs) of advective solute travel time through the unsaturated and the saturated zone of the transport domain. A nonstationary travel time pdf is derived for the saturated zone, to account for possible effects of flow nonuniformity due to recharge of water from the unsaturated zone. Nonuniform mean flow in the saturated zone decreases the relative influence of spatial variability within that zone on the ensemble mean solute breakthrough curve. Factors such as the longitudinal extent of the solute source and the unsaturated zone variability become more important for the spreading of the expected solute breakthrough as the degree of flow nonuniformity in the saturated zone increases. This implies that possible far‐field simplifications based on the assumption that the transport process in an integrated soil‐groundwater system is dominated by the transport conditions in the saturated zone may not be valid in cases with significant groundwater recharge from the unsaturated zone.

Renal amino acid transport in adults with oxidative phosphorylation diseases

The clinical manifestations of mitochondrial DNA (mtDNA) mutations depend on a variety of factors including ratios of normal to abnormal mtDNA and tissue-specific differences in ATP production by oxidative phosphorylation (OXPHOS). In order to investigate the effects of OXPHOS defects on renal tubule function, we characterized sodium-coupled transport processes in six individuals with OXPHOS diseases. Pathogenic mtDNA mutations were identified in five of these individuals. Sodium coupled transport processes were evaluated by determining fractional excretions of amino acids, glucose, lactate, urate, and phosphate in patients and controls. Four of the six individuals had high fractional excretions of neutral amino acids, indicating abnormal renal tubule reabsorbtion of these amino acids. Abnormalities in fractional excretions of lactate, glucose, urate, and phosphate were less pronounced. These results demonstrate that sodium-coupled transport processes in the kidney are sensitive to OXPHOS impairment. When abnormalities in these processes are encountered, an OXPHOS disease should be included in the differential diagnosis.

FINITE ELEMENT ANALYSIS OF COUPLED HEAT. MASS, AND PRESSURE TRANSFER IN POROUS BIOMATERIALS

Abstract The finite element method was used to solve Luikov's system of partial differential equations for neat, mass, and pressure transfer in capillary porous bodies. The finite element predictions were validated by comparing with exact solutions and the analytical results given by Mikhailov and Shishedjiev [1]. An application of the finite element method to the drying of wood (spruce) and a comparison based on an eigenvalue solution for simultaneous heat and mass transfer [2] are also provided. This technique was applied to study the coupled transport process in a silicon gel. The simulation indicated that the results obtained from the heat, mass, and pressure transfer model showed a marked difference from the results obtained by the heat and mass transfer model.

Amiloride inhibition of angiogenesis in vitro.

Angiogenesis is important to such processes as normal embryonic development and tissue growth, and is also a central feature of diseases such as diabetic retinopathy and the growth of solid tumors. Understanding the basic events governing angiogenesis has therefore attracted great interest. The ion channel blocking agent, amiloride, has been shown to inhibit angiogenesis in an in vivo model (Lansing et al., '91). This suggested a vital role for Na(+)-coupled transport processes in angiogenesis. A large number of structural analogues of amiloride have been synthesized (Kleyman and Cragoe, '88), and many of these are well characterized with respect to biological activity. These analogues present an opportunity to dissect the process of angiogenesis and identify potentially important physiological events. In this report we describe the effects of amiloride on an in vitro model for angiogenesis employing vascularized tissue explants. Amiloride inhibits capillary morphogenesis completely and reversibly at concentrations as low as 134 microM. It appears to act by blocking endothelial cell proliferation, but not migration. Inhibition is heightened by the introduction of hydrophobic groups on the terminal guanidino nitrogen atom, or on the 5-amino position. An analogue substituted at both of these positions is 30-fold more potent than the parent compound. Of amiloride's known biological activities, these results most closely correlate with the inhibition of Ca2+ transport processes, and thereby suggest an important role for Ca2+ transport in capillary morphogenesis.

New avenues in membrane science and technology

Recent advances and avenues for further research and development in three specific fields of membrane science and technology are reviewed. The potential of membrane processes for gas separation has been considerably improved by the development of new materials combining high permeability and selectivity. While working correlations between polymer structure and permeation characteristics have been evolved, there is need to further develop our basic understanding of this relationship. The second field reviewed is that of improving the separation characteristics of porous membrane filtration (ultra-/microfiltration). Recent promising approaches include the fabrication of membranes with uniform porosities, new module configurations and the manipulation of feed chemistries. The third area highlighted is that of hybrid membrane processes. These are considered both as integrated processes in which the membrane process operates in conjunction with another unit operation or as a coupled transport process in which the basic functioning of the membrane is intimately coupled with another physical or chemical process in single unit operation. The scope for basic research in these fields is indicated.

Experimental determination and numerical simulation of the permeability of cementitious materials

Safety analysis of a repository requires a detailed numerical study of the coupled transport processes of gas and water in the repository. Experimental studies were carried out to measure the transport parameters of different types of normal concrete. The capillary pressure curve, the gas and the water permeabilities were determined in separate experiments. Especially the influence of the water content of the samples was under investigation. Additionally coupled gas and water flow experiments were carried out and numerically simulated with the measured transport parameters. With the relative permeability curve and the experimental determined pore size distribution it is possible to describe the coupled transport of gas and water through specimens.

Isothermal Coupled Transport Process across Clay Membrane

Isothermal Coupled Transport Process across Clay Membrane

Coupling coefficients for two-phase flow in pore spaces of simple geometry

Here it is acknowledged that analytical descriptions of idealized two-phase flow of immiscible fluids in certain capillary pore spaces (e.g. those shaped like cylinders and cracks) actually are quite easy to derive. Such flow also can be regarded as primitive examples of coupled transport processes. As such, they may be employed to serve as models of how comparable processes probably occur in real porous media of complex pore structure. While the degree of coupling to be expected for all transport systems inherently is a question that ultimately must be answered by making experimental observations, qualitative indications also can come from model studies such as the ones presented in this paper. The main conclusion drawn from the work reported herein is that ambiguities can result whenever coupling effects arbitrarily are ignored just because direct measurements are too difficult or inconvenient to obtain.

Coupled Transport Processes across Clay Membranes

Coupled transport process involving passage of water and aqueous electrolytes across bentonite and kaolinite clay membranes in different cationic forms, as well as a clay humate membrane has been studied, under both isothcimal and non-isothermal conditions. Specially designed osmotic cells have been fabricated for the purpose and used. The experimental data have been fitted to formulations developed on the frame-ork of non-equilibrium thermodynamics to yield the appropriate reflection coefficient and heat of transport values for various membrane transport systems. An attempt has been made to interpret these values in terms of structural modifications in clay-sorbed water, ensuing from the clay-water interactions, as compared to the bulk water state.

Energetics of sodium-coupled active transport mechanisms in invertebrate epithelia.

The Na+ gradient has been implicated as the sole or primary energy source for accumulative transport of organic solutes (e.g., sugars, amino acids) across the mucosal membrane of a variety of epithelial cells. A basic question concerning the Na+-coupled transport process in epithelia is whether the energy available from the transmucosal Na+ electrochemical difference is sufficient to sustain an accumulated organic solute steady-state level. Measurements of Na+ activities, with Na+-sensitive microelectrodes, gave accurate estimates of the Na+ electrochemical potential difference across the mucosal membrane of Aplysia californica gut. The results suggest that the transmucosal Na+ gradient can furnish sufficient energy to sustain the observed intracellular levels of the cotransported species. Many other species sustain large intracellular-extracellular gradients (less than 10(6):1) of free solutes. Theoretical models suggest that secondary active transport mechanisms in these epithelia operate by energetic multiple coupling to the Na+ electrochemical gradient; coupling coefficients of approximately 3 may represent an evolutionary optimization of these epithelial cotransporters. To properly investigate the cotransport mechanisms and energetics in invertebrate membranes, prototype mammalian vesicle experiments should be extended to the invertebrate laboratory.