Diffusion-related molecular processes

The diffusion-related molecular processes occurring within a Cig stationary-phase have also been investigated using pyrene as a fluorescent probe [169]. Particular spectral bands were attributed to pyrene excimers formed in a diffusion-limited reaction. Rate constants for this formation were then used to estimate the microviscosity of the stationary-phase. A similar application of total internal reflection fluorescence... 

Viscous stress is an extremely important variable, and this quantity is identified by the Greek letter r. Viscous stress represents molecular transport of momentum, analogous to heat conduction and diffusion. All molecular transport mechanisms correspond to irreversible processes that generate entropy under realistic conditions. When fluids obey Newton s law of viscosity, there is a linear relation between viscous stress and velocity gradients. All fluids do not obey Newton s law of viscosity, but almost aU gases and low-molecular-weight liquids are Newtonian. 

The development of micro-chromatography systems has been motivated by the fact that as the system size is reduced, its performance is improved. The improvements that include reduction in analysis time and increase in separation efficiencies are a direct consequence of miniaturization as described in Janasek et al. (see Further Reading) and summarized here. The benefits of miniaturization can be demonstrated considering proportionalities within the system. We assume that miniaturization is a three-dimensional downscaling process characterized by a typical length parameter d. The separation system is a diffusion-related system in which hydro-dynamic, heat and molecular diffusion behave exactly... 

The characters of single-component model are as follow.23i (l) a key component is selected to be used for the estabhshment of mass balance for diffusions and reaction processes in catalyst particle, and the variation of molecular fraction for other reaction components is used for finding the relation with key component according to stoichiometric equations ... 

As examined in the next chapter, transition-state theory is applicable when the rate-limiting step of a molecular process is controlled by a slow passage over a barrier. Not only reactions but also some diffusion processes are characterized by equilibration of a molecule on a surface site, in a cavity of a zeolite, and by movement of a molecule over a barrier (Figure 4.17). For diffusion, the relation between distance of motion and time is given by... 

This chapter is concerned with molecular diffusion-related chemical transport parameter estimation procedures at the water-sediment interface. Transport coefficients for particle resuspension and settling are in Chapter 10. Chapter 11 is concerned with the bed porewater advective process and Chapter 13 covers macrofauna driven... 

The orientation of linear rotators in space is defined by a single vector directed along a molecular axis. The orientation of this vector and the angular momentum may be specified within the limits set by the uncertainty relation. In a rarefied gas angular momentum is well conserved at least during the free path. In a dense liquid it is a molecule s orientation that is kept fixed to a first approximation. Since collisions in dense gas and liquid change the direction and rate of rotation too often, the rotation turns into a process of small random walks of the molecular axis. Consequently, reorientation of molecules in a liquid may be considered as diffusion of the symmetry axis in angular space, as was first done by Debye [1],... 

Since in most situations the perturbation quantities (V and c() are not explicitly resolved, it is not possible to evaluate the turbulent flux term directly. Instead, it must be related to the distribution of averaged quantities - a process referred to as parameterization. A common assumption is to relate the turbulent flux vector to the gradient of the averaged tracer distribution, which is analogous with the molecular diffusion expression. Equation (35). 

---