External concentration

The 0.865 factor is used to match this equation to the Brenner and Gaydos expression for = 0.2. In these cases, the pore concentration Cpi is related to the external concentration Cj by the partition ratio... 

In spite of these difficulties the available data on crop performance (see Table 1) shows that the external concentration at which yield reduction becomes critical varies according to the crop. The approach to improving the salt resistance depends upon the external concentration at which improvement is sought. 

Moderate soil salt concentration. These are external concentrations at which substantial osmotic adjustment in the plant is required, and could not be achieved with NaCl without compartmentation between cytoplasm and vacuole. Damage may still be attributable to excessive internal concentrations, but simply minimising salt uptake is not a sufficient answer. The concentration of osmotically active solutes within the cells has to be... 

Soillroot interactions. High external concentrations make the acquisition of water and nutrients difficult because of the low water potential of the soil solution, and of chemical competition between saline and nutrient ions. 

The external concentration is known, and the concentration profile throughout the slab is symmetrical,... 

Here Sq is the external substrate concentration and AX is the length of the finite difference element. Boundary conditions are given by the external concentrations Sq and Pq and by setting Sn+i = Sn and Pn+1 - Pn. at the slab centre. 

T. Ingestad, Relative addition rate and external concentration driving variables used in plant nutrition research. Plant Cell Environ. 5 443 (1982). 

Thus, at equilibrium, the transbilayer concentration gradient of the weak acid reflects the inverse of the transbilayer concentration gradient of protons (Fig. 14). For example, a pH difference of 2 units (e.g., internal pH = 9 and external pH = 7) shoud lead to 100-fold higher concentration of weak acid within the vesicle as compared to the external concentration. 

In the limit of low effectiveness factors where tj becomes inversely proportional to the Thiele modulus, the apparent order of the reaction may differ from the true order. In this case, since the rate is proportional to the product of the effectiveness factor and the external concentration... 

In summary, our analysis indicates that intraparticle temperature gradients and external concentration gradients are clearly negligible while intraparticle concentration gradients are clearly significant. External temperature gradients do exist, but they are small. 

Consider a concentration gradient for NaCl with an internal protocell concentration of 150 mM and an external concentration of order 1 mM, as might be found in a freshwater environment. There is a membrane potential of —200 mV. 

The soil aggregates are assumed to be spherical in form and to have constant temperature and to contain initially uniform distributions of substrate (contaminant) and biomass. The external concentrations of biomass and substrate are assumed to be zero and the external oxygen concentration is constant. Substrate is adsorbed onto the solid phase to an extent determined by an equilibrium partition coefficient. 

K+ is accnmnlated in both the cytosol and vacuole by passive diffusion, except when the external concentration is small in which case its is actively taken up ... 

A particular ion or uncharged molecule can be transported by different transporters depending on its concentration. For example NH4+ may be absorbed by a passive low-affinity uptake system when its external concentration is large and by an active high-affinity system when its external concentration is small. Figure 6.10 summarizes the main transport processes on the plasma membrane and tonoplast of plant cells. 

The aim is to measure the influx of the nutrient into a root for a given concentration of the nutrient in the soil solution at the root surface. This is a seemingly simple matter. But there are well-known difficulties in obtaining unequivocal information (Marschner, 1995 Tinker and Nye, 2000). The main problem is that the influx of the nutrient is closely regulated by the plant and depends sensitively on the current nutrient content of the plant as well as the external concentration the root is exposed to. Over time the plant will adjust its intake to the new external concentration, so the measured influx will be a function of how long the plant has been exposed to the new concentration. Measurements should therefore be made as rapidly as possible following exposure to the new concentration. 

Concentration polarization is a major problem in PRO. External concentration polarization occurs in the liquid boundary layers on either side of the membrane. External concentration polarization can be minimized by stirring the solutions to reduce the thickness of these boundary layers. 

Glucose derived from glycogen stores or made in gluconeogenesis is transported out of liver cells to increase blood glucose when the external concentration is low. 

When mass diffuses into or out of a fluid particle, the concentration within the particle changes with time. Therefore the time derivatives must be retained in the diffusion equations for both internal and external fluids. The internal and external concentration fields are related at the interface. If there is no... 

When the internal resistance is negligible, the particle concentration is uniform and its time variation can be related to the external concentration gradient by a mass balance on the diffusing species ... 

No construction joint leaks or intrusion through open doors should exceed 0.1% of the measured external concentration. See Tables 6 and 7. 

Furthermore, V > 0 is the voltage drop in the system (between x = 0 — 0 and x — L + 0) 0 < Co 1 is the external concentration of univalent electrolyte (equilibrium concentration of electrons and holes), maintained fixed at the outer boundaries of the multilayered arrangement. 

Therefore, the cell is very vulnerable to changes in intracellular Ca2+ concentration, which are maintained at a very low level, 100 nM (0.1 pM) relative to the external concentration, 1 mM. To maintain this 10,000-fold difference requires energy. There are specific pumps, which pump Ca2+ out of the cell, or into the lumen of the endoplasmic reticulum where concentrations may reach 100 pM, or into the mitochondria, which is a lower-affinity system and is normally less important. 

Figure 19.18 shows how for different values of y sorption proceeds as a function of the nondimensional time t defined by Eq. 19-79. As y increases from the infinite bath case, we see that the time required to reach equilibrium decreases. This can be understood by recognizing that while the chemical is diffusing into the sphere, the concentration in the surrounding fluid drops. Hence, the total mass exchange needed to attain equilibrium between the fluid and the sphere is smaller than in the infinite bath case in which the external concentration remains constant. 

In order to evaluate the rate constants from the analysed sugar concentrations, we need information on the amount of sugar present in the ionized form inside the ion-exchanger as a function of these external concentrations. These relations have been determined separately and we previously reported on ionisation (ref.8) and adsorption (ref.9). Using these relations rate constants were calculated from initial rate data (ref.5) and the results will be presented in the following sections. 

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