Water conductivity coefficient

When the water potential inside a cell differs from that outside, water is no longer in equilibrium and we can expect a net water movement from the region of higher water potential toward the region of lower water potential. This volume flux density of water, Jyw> is generally proportional to the difference in water potential (AY) across the membrane or membranes restricting the flow. The proportionality factor indicating the permeability to water flow at the cellular level is expressed by a water conductivity coefficient, L,1 ... 

When Equation 2.26 is applied to cells, Y° is the water potential in the external solution, and Y1 usually refers to the water potential in the vacuole. Lw then indicates the conductivity for water flow across the cell wall, the plasma membrane, and the tonoplast, all in series. For a group of barriers in series, the overall water conductivity coefficient of the pathway, L,., is related... 

When the value of the water conductivity coefficient is known, the water potential difference necessary to give an observed water flux can be calculated using Equation 2.26. For the internodal cells of Cham and Nitella, Am for water entry is about 7 x 10-13 m s-1 Pa-1. For convenience of calculation, we will consider cylindrical cells 100 mm long and 1 mm in diameter as an approximate model for such algal cells (see Fig. 3-13). The surface area across which the water flux occurs is 2nrl, where r is the cell radius and / is the cell length. Thus the area is... 

A spherical algal cell 1 mm in diameter has a water conductivity coefficient... 

We note that Lp is essentially the same as and hence usually replaces Lw, the water conductivity coefficient that we introduced in Chapter 2 (e.g., in Eqs. 2.26 and 2.35 see Fig. 3-19). In the absence of a hydrostatic pressure... 

An overview of some basic mathematical techniques for data correlation is to be found herein together with background on several types of physical property correlating techniques and a road map for the use of selected methods. Methods are presented for the correlation of observed experimental data to physical properties such as critical properties, normal boiling point, molar volume, vapor pressure, heats of vaporization and fusion, heat capacity, surface tension, viscosity, thermal conductivity, acentric factor, flammability limits, enthalpy of formation, Gibbs energy, entropy, activity coefficients, Henry s constant, octanol—water partition coefficients, diffusion coefficients, virial coefficients, chemical reactivity, and toxicological parameters. 

Atterberg-limit tests determine the water content influence in defining liquid, plastic, semisolid and solid states of fine-grained soils. Permeability tests may be carried out in the laboratory or in the field. Such tests are used to determine the hydraulic conductivity coefficient k. ... 

Figure 12. Water self-diffusion coefficient of Nafion 117 (EW =1100 g/equiv), as a function of the water volume fraction Xy and the water diffusion coefficient obtained from a Monte Carlo (MC) simulation (see text). The proton conductivity diffusion coefficient (mobility) is given for comparison. The corresponding data points are displayed in Figure 14.

Molecular Size of the Compounds The size and molecular length of the PPCP compound can also influence the efficacy of the membrane. Molecular length is, in this instance, defined as the maximum length of the molecule, whereas molecular width refers to its cross-sectional diameter. Kimura et al. (2003) tested 11 neutral pharmaceutically active compounds that greatly vary in molecular weight, octanol-water partition coefficients (Xqw), and dipole moments for regeneration by two distinctly different RO membranes. AU of the assays were conducted at 20°C (pH 7 + 0.1) and filtration was done over a 24-h period. A key assumption from that experiment was that by the end of that duration, the membrane was saturated. The percent regeneration K) of the compound by the membrane was calculated from... 

The simulations of volatilization were conducted using the complete model described by Jury et al. (33) where each chemical is present in the soil at a uniform concentration of 1 kg/ha to a depth, L, in the soil and is allowed to volatilize through a stagnant air boundary layer for a specified time period in the presence or absence of water evaporation. The standard conditions or common properties assumed in the simulations are the same as those indicated in Jury et al. (35, 36), i.e., air diffusion coefficient, 0.43 m /d water diffusion coefficient, 4.3 X 10-3 m /d atmospheric relative humidity, 50% temperature, 25°C soil porosity, 50% bulk density, 1.35 g/cm3 soil water content, 0.30 organic carbon fraction, 0.0125 amount of pesticide in soil, 1 kg/ha depth in soil, 1 or 10 cm water evaporation rate, 0, 0.25, or 0.50 cm/d. 

LP is the hydraulic conductivity coefficient and can have units of m s-1 Pa-1. It describes the mechanical filtration capacity of a membrane or other barrier namely, when An is zero, LP relates the total volume flux density, Jv, to the hydrostatic pressure difference, AP. When AP is zero, Equation 3.37 indicates that a difference in osmotic pressure leads to a diffusional flow characterized by the coefficient Lo Membranes also generally exhibit a property called ultrafiltration, whereby they offer different resistances to the passage of the solute and water.14 For instance, in the absence of an osmotic pressure difference (An = 0), Equation 3.37 indicates a diffusional flux density equal to LopkP. Based on Equation 3.35, vs is then... 

LP (hydraulic conductivity coefficient) K (water permeability coefficient) Minor both indicate water permeability... 

B. Suppose that there are four plants/m2 of ground and that their stem diameter is 3 cm. If the thermal conductivity coefficient of the stem is the same as that of water, and the temperature changes from that of the bulk of the vegetation to that of the ground in 0.8 m, what is the rate of heat conduction in W down each stem What is the average value of such Jh per m2 of the ground ... 

The initial emphasis on evaluation and modeling of losses in the membrane electrolyte was required because this unique component of the PEFC is quite different from the electrolytes employed in other, low-temperature, fuel cell systems. One very important element which determines the performance of the PEFC is the water-content dependence of the protonic conductivity in the ionomeric membrane. The water profile established across and along [106]) the membrane at steady state is thus an important performance-determining element. The water profile in the membrane is determined, in turn, by the eombined effects of several flux elements presented schematically in Fig. 27. Under some conditions (typically, Pcath > Pan), an additional flux component due to hydraulic permeability has to be considered (see Eq. (16)). A mathematical description of water transport in the membrane requires knowledge of the detailed dependencies on water content of (1) the electroosmotic drag coefficient (water transport coupled to proton transport) and (2) the water diffusion coefficient. Experimental evaluation of these parameters is described in detail in Section 5.3.2. 

Barbiturates. QSAR studies by Hansch presented evidence that the hypnotic activity of barbiturates depends largely on their relative lipophilic character as determined by octanol-water partition coefficients (102-104). Employing Equation 5.6, a QSAR analysis was conducted on over 100 barbiturates as well as a number of non-barbiturates having hypnotic activity. 

Physical Mechanisms. The simplest interpretation of these results is that the transport coefficients, other than the thermal conductivity, of the water are decreased by the hydration interaction. The changes in these transport properties are correlated the microemulsion with compositional phase volume 0.4 (i.e. 60% water) exhibits a mean dielectric relaxation frequency one-half that of the pure liquid water, and ionic conductivity and water selfdiffusion coefficient one half that of the bulk liquid. In bulk solutions, the dielectric relaxation frequency, ionic conductivity, and self-diffusion coefficient are all inversely proportional to the viscosity there is no such relation for the thermal conductivity. The transport properties of the microemulsions thus vary as expected from simple changes in "viscosity" of the aqueous phase. (This is quite different from the bulk viscosity of the microemulsion.)... 

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