Concentration-depth gradient

Several species have been shown to not modify S-320 or MAA concentration in response to UVR, such as the zoanthid Zoanthus sociatus, in response to increased levels of UVR [101], the octocoral Clavularia sp. over a depth gradient [51], the coral Montastraea annularis on transplantation from 24 m to 12 m over 21 days [102] and the temperate anemone Anthopleura elegantissima in UVR-exposed versus UVR-shielded experiments [53]. Data such as these have been used to suggest that MAAs are not directly photoprotective but are rather a byproduct of other chemical reactions and that photoprotection is a secondary function. An alternative explanation is that, at least for all of the above studies that involve coelenterates, the MAAs are derived from diet and therefore rather than MAA concentration being dependent on the intensity of UVR is dependent on the concentration of MAAs in the food source. 

Densities of upper and lower water mass identified in the cross-section. Diagrammatic concentration—depth profile at present approximated to well-mixed upper and lower layers, with a linear concentration gradient in the pycnocline layer. Initial concentration of dissolved solids 100 grams/liter in the upper layer assumed for the purpose of calculating the age of stratification as discussed in the text. 

To estimate the average gradient, the concentration difference should be divided by the unknown boundary layer depth 5. While this is unknown, the Carberry number (Ca) gives a direct estimate of what concentration fraction drives the transfer rate. The concentration difference tells the concentration at which the reaction is really running. 

The reflectivity for this simple case can be extended readily to more complex situations where there are concentration gradients in single films or multilayers comprised of different components. Basically the reflectivity can be calculated from a simple recursion relationship that effectively reduces any gradients in composition to a histogram representing small changes in the concentration as a function of depth. Details on this can be found in the literature cited. ... 

For such a condition of equilibrium to be reached, the atoms must acquire sufficient energy to permit their displacement at an appreciable rate. In the case of metal lattices, this energy can be provided by a suitable rise in temperature. In the application of coatings the diffusion process is arrested at a suitable stage when there is a considerable solute concentration gradient between the surface and the required depth of penetration. 

Porous electrodes are systems with distributed parameters, and any loss of efficiency is dne to the fact that different points within the electrode are not equally accessible to the electrode reaction. Concentration gradients and ohmic potential drops are possible in the electrolyte present in the pores. Hence, the local current density, i (referred to the unit of true surface area), is different at different depths x of the porous electrode. It is largest close to the outer surface (x = 0) and falls with increasing depth inside the electrode. 

The above second-order differential equation can be solved by integration. At the liquid surface, where Z=0, the bulk gas concentration, Cso. is known, but the concentration gradient dCs/dZ is unknown. Conversely at the full liquid depth, the concentration Cso is not known, but the concentration gradient is known and is equal to zero. Since there can be no diffusion of component S from the bottom surface of the liquid, i.e., js at Z=L is 0 and hence from Pick s Law dCs/dZ at Z=L must also be zero. 

The problem is thus one of a split boundary type, but one which can be solved by an iterative procedure based on an assumed value for one of the unknown boundary conditions. Assuming a value for dC /dZ at the initial condition Z=0, the equation can be integrated twice to produce values of dCs/dZ and Cs at the terminal condition, Z=L. If the correct value has been taken, the integration will lead to the correct boundary condition that dCs/dZ=0 at Z=L and hence the correct value of Cs- The value of the concentration gradient dCs/dZ is also obtained for all values of Z, throughout the depth of liquid. 

Chemical gradients Across Earth s layers of core solids Sea depth Atmosphere height Concentrations in liquids behind barriers... 

In order to answer the former question, how long does it take to change from the free to final steady-state exhalation, we must again consult detailed diffusion theory. It can be shown (Samuels-son, 1984) that the reshaping of the radon depth-concentration gradient is characterized by an exponential sum of the form... 

Within the depth-dependent redox gradient, concentration peaks of solid Fe(lll) and of dissolved Fe(II) develop, the peak of Fe(III) overlying the peak of Fe(II) ... 

---