Notes on Phenomenology

Divisek et al. presented a similar two-phase, two-dimensional model of DMFC. Two-phase flow and capillary effects in backing layers were considered using a quantitatively different but qualitatively similar function of capillary pressure vs liquid saturation. In practice, this capillary pressure function must be experimentally obtained for realistic DMFC backing materials in a methanol solution. Note that methanol in the anode solution significantly alters the interfacial tension characteristics. In addition, Divisek et al. developed detailed, multistep reaction models for both ORR and methanol oxidation as well as used the Stefan—Maxwell formulation for gas diffusion. Murgia et al. described a one-dimensional, two-phase, multicomponent steady-state model based on phenomenological transport equations for the catalyst layer, diffusion layer, and polymer membrane for a liquid-feed DMFC. 

Studies of the interfacial structure often quote early models from the first half of the twentieth century, and although these models have led to useful insights about the nature of the interface, it is important to note that they are based exclusively on phenomenological characteristics and macroscopic observations. To establish a rigorous understanding of the interfacial structure, microscopic data from experimental and theoretical studies (e.g., statistical mechanical and quantum mechanical) of the metal-water interface are needed. 

As we have already noted, the phenomenological picture of the transition from a = to a = lorO described above is actually based on the assumption that the activation energy changes monotonically although this postulate was initially not formulated. This monotonicity is illustrated by potential diagrams of the type shown in Figure 1.8 where the energy is plotted as a function of a certain reaction coordinate X. 

Theoretical models of the film viscosity lead to values about 10 times smaller than those often observed [113, 114]. It may be that the experimental phenomenology is not that supposed in derivations such as those of Eqs. rV-20 and IV-22. Alternatively, it may be that virtually all of the measured surface viscosity is developed in the substrate through its interactions with the film (note Fig. IV-3). Recent hydrodynamic calculations of shape transitions in lipid domains by Stone and McConnell indicate that the transition rate depends only on the subphase viscosity [115]. Brownian motion of lipid monolayer domains also follow a fluid mechanical model wherein the mobility is independent of film viscosity but depends on the viscosity of the subphase [116]. This contrasts with the supposition that there is little coupling between the monolayer and the subphase [117] complete explanation of the film viscosity remains unresolved. 

In addition to the main six experimental observations mentioned at the beginning of this Section, some other phenomenological features of the ECT of the cancerous tumors (e.g., grown on the rat skins) have been also noted, as follows 37... 

This is identical to the Spiegler-Kedem relationship, Eq. (2), and that of finely-porous membrane model, Eq. (3), with a = r. However, it should be noted that Eq. (28) is derived phenomenologically without any assumptions on the transport mechanism. 

As noted by Carberry in 1987, only phenomenological values can be measured in the laboratory since it is not possible to a priori distinguish between A (the catalytic area) and A (exposed measurable area), per volume of catalyst agent. This yields a structure-sensitive reaction that is dependent on crystallite size. While it is clear that a mechanism cannot be determined from purely kinetic measurements, a proposed mechanism is only accepted after it can predict the observed kinetic measurements. The dominant issue of the observed measurements is whether A or A is being measured. This correct measurement will yield the proper intrinsic kinetics, but will not reveal much insight into the mechanism. Thus, it is imperative to identify and obtain as much information as possible on the nature of intermediate chemical species. 

Trichotillomania, listed in the DSM-IV under Impulse Control Disorders Not Elsewhere Classified ( 252), is characterized by impulses to pull out one s hair, often involving multiple sites (scalp, eyebrows, and eyelashes commonly pubic, axillary, chest, and rectal areas less commonly) ( 253). Some clinicians have proposed that this condition is a variant of OCD, based on similarities in phenomenology, family history, and response to treatment. Originally thought to occur more frequently in females, it has become evident that it may affect males just as often. Many victims of this disorder have histories beginning in childhood and refractoriness to all attempted remedies. Co-morbidity of trichotillomania with mood, anxiety, substance abuse, and eating disorders is also common (254). Others have noted that trichotillomania may also coexist with mental retardation and psychotic disorders (see Appendix Q). 

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