Ionic flux

The advantages of this type of system are that the release rates are independent of the dmg properties, macromolecules and ionic species may be dehvered, fluxes may be high, and release rates are not dependent upon environmental conditions such as pH. The disadvantages are that the system is subject to dose-dumping if it is chewed. It is also more expensive to formulate than coating tablets, and there is a possibiUty of hole plugging. 

These three terms represent contributions to the flux from migration, diffusion, and convection, respectively. The bulk fluid velocity is determined from the equations of motion. Equation 25, with the convection term neglected, is frequently referred to as the Nemst-Planck equation. In systems containing charged species, ions experience a force from the electric field. This effect is called migration. The charge number of the ion is Eis Faraday s constant, is the ionic mobiUty, and O is the electric potential. The ionic mobiUty and the diffusion coefficient are related ... 

For electrolytic solutions, migration of charged species in an electric field constitutes an additional mechanism of mass transfer. Thus the flux of an ionic species Nj in (g mol)/(cm s) in dilute solutions can be expressed as... 

The ionic mobility is the average velocity imparted to the species under the action of a unit force (per mole), i is the stream velocity, cm/s. In the present case, the electrical force is given by the product of the electric field V in V/cm and the charge per mole, where S" is the Faraday constant in C/g equivalent and Z is the valence of the ith species. Multiplication of this force by the mobihty and the concentration C [(g mol)/cm ] yields the contribution of migration to the flux of the ith species. 

On substituting diese values into the ionic flux equations we obtain... 

In the case of systems containing ionic liquids, components and chemical species have to be differentiated. The methanol/[BMIM][PF6] system, for example, consists of two components (methanol and [BMIM][PFg]) but - on the assumption that [BMIM][PFg] is completely dissociated - three chemical species (methanol, [BMIM] and [PFg] ). If [BMIM][PFg] is not completely dissociated, one has a fourth species, the undissociated [BMIM][PFg]. From this it follows that the diffusive transport can be described with three and four flux equations, respectively. The fluxes of [BMIM] ... 

The most important driving forces for the motion of ionic defects and electrons in solids are the migration in an electric field and the diffusion under the influence of a chemical potential gradient. Other forces, such as magnetic fields and temperature gradients, are commonly much less important in battery-type applications. It is assumed that the fluxes under the influence of an electric field and a concentration gradient are linearly superimposed, which... 

Antiarrhythmic Drugs. Figure 1 Transmembrane ionic currents of the cardiac action potential. In the middle of the figure, a typical cardiac action potential is shown as can be obtained from the ventricular myocardium (upper trace). Below, the contribution of the various transmembrane currents is indicated. Currents below the zeroline are inward currents above the zero line are outward fluxes. In the left column the name of the current is given and in the right column the possible clone redrawn and modified after [5]. 

The mechanisms that affect heat transfer in single-phase and two-phase aqueous surfactant solutions is a conjugate problem involving the heater and liquid properties (viscosity, thermal conductivity, heat capacity, surface tension). Besides the effects of heater geometry, its surface characteristics, and wall heat flux level, the bulk concentration of surfactant and its chemistry (ionic nature and molecular weight), surface wetting, surfactant adsorption and desorption, and foaming should be considered. 

Ca may activate phospholipase A2 and cause production of lyso-lipids and fatty acids. In addition, ionic fluxes across the membrane occur, leading to pH changes and membrane depolarization. It is not clear how these other responses are initiated, but there may be direct G-protein links to effector systems such as phospholipase A2 or ionic channels. 

Figure 1. Simplified schematic of receptor-mediated signal transduction in neutrophils. Binding of ligand to the receptor activates a guanine-nucleotide-binding protein (G protein), which then stimulates phospholipase C. Phosphatidylinositol 4,5-bis-phosphate is cleaved to produce diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). DAG stimulates protein kinase C. IP3 causes the release of Ca from intracellular stores, which results in an increase in the cytosolic Ca concentration. This increase in Ca may stimulate protein kinase C, calmodulin-dependent protein kinases, and phospholipase A2. Protein phosphorylation events are thought to be important in stimulating degranulation and oxidant production. In addition, ionic fluxes occur across the plasma membrane. It is possible that phospholipase A2 and ionic channels may be governed by G protein interactions. ...

IONIC TRANSPORT BY MIGRATION AND DIFFUSION 4.3.1 Equations for the Total Flux... 

Solute Flux Solute partitioning between the upstream polarization layer and the solvent-filled membrane pores can be modeled by considering a spherical solute and a cylindrical pore. The equilibrium partition coefficient 0 (pore/bulk concentration ratio) for steric exclusion (no long-range ionic or other interactions) can be written as... 

The elementary step of ion transfer is considered to take place between positions x and X2, and therefore the electrical potential drop affecting this transfer is Ao02- The ion transfer involves the renewal of the solvation shell. The change in standard chemical potential Ao f associated with this process takes place over very short distances in the interfacial region [51] and can be assumed to occur between positions X2 and x - Thus, the BV equation for the flux density /, of an ionic species i is [52]... 

Fluorescence-based methods do not directly measure ionic current but, rather, measure either membrane-potential-dependent or ion-concentration-dependent changes of fluorescence signals (from fluorescent dyes loaded into the cytosol or cell membrane) as a result of ionic flux. Because fluorescence-based methods give robust and homogeneous cell population measurement, these assays are relatively easy to set up and achieve high throughput. 

Consider a dilute electrolyte solution containing s components (nonelectrolytes and various ionic species) in which concentration gradients of the components and an electric field are present. The material flux of the ith component is then given by a combination of Eqs (2.3.11) to (2.3.20) ... 

Since the ionic fluxes cannot be measured individually, it is preferable to introduce the salt flux, besides solvent flux and charge flux (current density). The driving forces would then be the gradients or differences of the chemical potentials in media with different salt concentrations and different pressures, multiplied by -1. These differences must be relatively small to remain within the framework of linear irreversible thermodynamics, so that... 

Electrodialysis is a process for the separation of an electrolyte from the solvent and is used, for example, in desalination. This process occurs in a system with at least three compartments (in practice, a large number is often used). The terminal compartments contain the electrodes and the middle compartment is separated from the terminal compartments by ion-exchanger membranes, of which one membrane (1) is preferentially permeable for the cations and the other one (2) for the anions. Such a situation occurs when the concentration of the electrolyte in the compartments is less than the concentration of bonded ionic groups in the membrane. During current flow in the direction from membrane 1 to membrane 2, cations pass through membrane 1 in the same direction and anions pass through membrane 2 in the opposite direction. In order for the electrolyte to be accumulated in the central compartment, i.e. between membranes 1 and 2 (it is assumed for simplicity that a uni-univalent electrolyte is involved), the relative flux of the cations with respect to the flux of the solvent, /D +, and the relative flux of the anions with respect to... 

Ion transport across membranes can be evaluated by using mucosal and serosal electrodes to read transepithelial current (I) and potential difference OP). With these parameters, equivalent circuit analysis can be utilized to account for the relative contributions of transcellular and paracellular pathways. Ionic flux (J) is defined by the Nernst-Planck equation,... 

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