Transport dependent models

Generally, the transport parameter used is the logarithm of the partition coefficient of the bas (bioactive substance) or some quantity derived from it. The partition coefficient is almost always determined between water and 1-octanol. Parameters obtained by chromatographic methods are being used with increasing frequency however. The term in t2 is introduced to account for the frequently observed parabolic dependence of a data set of bas on the transport parameter. Models other than... 

When a solute is transferred from a solid into a high-pressure gas, it is then taken downstream in the bulk fluid by convective transport. Depending on turbulence, the solute may travel further by other mass-transport mechanisms such as dispersion. Dispersion spreads the solute axially and radially in a cylindrical stet. Eaton and Akgerman [30] considered both axial and radial effects in a model for the desorption of heavy organics, from carbon, by a dense gas. 

The rate and characteristics of surface evolution depend on the particular transport mechanisms that accomplish the necessary surface motion. These can include surface diffusion, diffusion through the bulk, or vapor transport. Kinetic models of capillarity-induced interface evolution were developed primarily by W.W. Mullins [1-4]. The models involving surface diffusion, which relate interface velocity to fourth-order spatial derivatives of the interface, and vapor transport, which relate velocity to second-order spatial derivatives, derive from Mullins s pioneering theoretical work. 

Experimental results presented in this work and in the literature are inconsistent with the assumptions and the physical interpretations implicit in the dual-mode sorption and transport model, and strongly suggest that the sorption and transport in gas-glassy polymer systems should be presented by a concentration-dependent model ... 

The concentration-dependent models attribute the observed pressure dependence of the solubility and diffusion coefficients to the fact that the presence of sorbed gas in a polymer affects the structural and dynamic properties of the polymer, thus affecting the sorption and transport characteristics of the system (3). On the other hand, in the dual-mode model, the pressure-dependent sorption and transport properties arise from a... 

The film thickness represents a model parameter that can be estimated using mass transfer coefficient correlations. These correlations reflect the mass transport dependence on physical properties and process hydrodynamics and are available from the literature (see, e.g., Refs. 57, 68 and 90). 

Himmelblau [32] and Himmelblau and Bischoff [33] have considered three types of model which are useful in process analysis, i.e. empirical models, population balance models and transport phenomena models. Empirical models involve mathematical relationships between dependent and independent variables, which are postulated either entirely a priori, or by considering the nature of the experimental data, or by analogies, etc. On the other hand, transport phenomena models are based on the laws of... 

The Mean Transport Pore Model (MTPM) described diffusion and permeation the model (represented as a boundary value problem for a set of ordinary differential equations) are based on Maxwell-Stefan diffusion equation and Weber permeation law. Parameters of MTPM are material constants of the porous solid and, thus, do not dependent on conditions under which the transport proeesses take place. 

The first important simplification is to combine the Bodenstein (Bo ) and modified Stanton (St, lli) numbers into a more common parameter in practice, i.e. the number of stages N . A more detailed derivation of the number of stages for a transport-dispersive model in dependency of Bo and St ff, can be found in Eq. 6.140. 

Depending on the main cause of sluggishness in reaching equilibrium in the column, we can distinguish several kinetic models. If the kinetics of the retention mechanism (e.g., the kinetics of adsorption-desorption) is slower than the other steps of the chromatographic process, we use the reaction-dispersive model. If the slowest step in the chromatographic process is the mass transfer kinetics, we have the transport-dispersive model. 

Models that are used to predict transport of chemicals in soil can be grouped into two main categories those based on an assumed or empirical distribution of pore water velocities, and those derived from a particular geometric representation of the pore space. Velocity-based models are currently the most widely used predictive tools. However, they are unsatisfactory because their parameters generally cannot be measured independently and often depend upon the scale at which the transport experiment is conducted. The focus of this chapter is on pore geometry models for chemical transport. These models are not widely used today. However, recent advances in the characterization of complex pore structures means that they could provide an alternative to velocity based-models in the future. They are particularly attractive because their input parameters can be estimated from independent measurements of pore characteristics. They may also provide a method of inversely estimating pore characteristics from solute transport experiments. 

Mishra, S., and J.C. Parker. 1990. Analysis of solute transport with a hyperbolic scale-dependent model. Hydrol. Process. 4 45-57. 

Toxicants towards Daphnia, as for those against fish, divide into those with non-specific effects and a heterogeneous group with specific effects, although the respective classifications for the different aquatic species do not necessarily coincide. The toxicity of the non-specific contaminants is related to their lipophilicity as expressed by log indicating (as for fish) the predominance of transport phenomena and the relevance of partitioning and hydrophobic membrane interractions for this mechanism of toxic action. As for the fish baseline QS ARs for non-polar non-reactive chemicals (section 5.1), log P -dependent models have been derived to describe Daphnia lethality, immobilization of the test animals or inhibition of their growth (Table 5.6). 

Moreover, a time-dependent model which has some of these properties is the PSACOIN Level-E geosphere transport model. Some results on the SA of this complex model are also reported. 

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