Explanation system

An interpreter, or explanation system, forms the interface between the user and the core software. It interprets queries from the user so that the inference engine can make sense of them and presents the conclusions of the inference engine in language appropriate to the needs and level of knowledge of the user. It is also responsible for generating explanations of the reasoning that... 

Together, the user interface and the explanation system, therefore, are important components in the ES. A user who finds the software difficult to use, or confusing, may become irritated with the system or be misled by it and stop using it. Worse still, they may misinterpret the advice that it provides. 

More radically, it can be argued that chemists recognized before most physicists the conventional character of the basic definitions and premises of scientific explanation systems, an argument usually identified in physics with Heinrich Hertz, Henri Poincare, and Edouard LeRoy at the end of the nineteenth century. And finally, chemists recognized early on that multiple explanations are superior to a simple but wrong explanation. In short, chemistry had a principle of complementarity long before physics did. 

But Ingold s triumph came in finally seeing the advantages of Robinson s explanation system, revising it, and substituting a new and clearer language and classification of types of reaction mechanisms. Lapworth, Robinson, and their collaborators referred to Ingold s "conversion" experience, a conversion in which Paul eventually helped create the myth of his role not as saint but as savior. 

There are numerous references in the literature to irreversible adsorption from solution. Irreversible adsorption is defined as the lack of desotption from an adsoibed layer equilibrated with pure solvent. Often there is no evidence of strong surface-adsorbate bond formation, either in terms of the chemistry of the system or from direct calorimetric measurements of the heat of adsorption. It is also typical that if a better solvent is used, or a strongly competitive adsorbate, then desorption is rapid and complete. Adsorption irreversibility occurs quite frequently in polymers [4] and proteins [121-123] but has also been observed in small molecules and surfactants [124-128]. Each of these cases has a different explanation and discussion. 

Irreversible adsorption discussed in Section XI-3 poses a paradox. Consider, for example, curve 1 of Fig. XI-8, and for a particular system let the equilibrium concentration be 0.025 g/lOO cm, corresponding to a coverage, 6 of about 0.5. If the adsorption is irreversible, no desorption would occur on a small dilution on the other hand, more adsorption would occur if the concentration were increased. If adsorption is possible but not desorption, why does the adsorption stop at 6 = 0.5 instead of continuing up to 0 = 1 Comment on this paradox and on possible explanations. 

The accepted explanation for the minimum is that it represents the point of complete coverage of the surface by a monolayer according to Eq. XVII-37, Sconfig should go to minus infinity at this point, but in real systems an onset of multilayer adsorption occurs, and this provides a countering positive contribution. Some further discussion of the behavior of adsorption entropies in the case of heterogeneous adsorbents is given in Section XVII-14. 

It is not surprising, in view of the material of the preceding section, that the heat of chemisorption often varies from the degree of surface coverage. It is convenient to consider two types of explanation (actual systems involving some combination of the two). First, the surface may be heterogeneous, so that a site energy distribution is involved (Section XVII-14). As an example, the variation of the calorimetric differential heat of adsorption of H2 on ZnO is shown in Fig. 

The thennalization stage of this dissociation reaction is not amenable to modelling at the molecular dynamics level becanse of the long timescales required. For some systems, snch as O2 /Pt(l 11), a kinetic treatment is very snccessfiil [77]. However, in others, thennalization is not complete, and the internal energy of the molecnle can still enliance reaction, as observed for N2 /Fe(l 11) [78, 79] and in tlie dissociation of some small hydrocarbons on metal snrfaces [M]- A detailed explanation of these systems is presently not available. 

Tunnelling is a phenomenon that involves particles moving from one state to another tlnough an energy barrier. It occurs as a consequence of the quantum mechanical nature of particles such as electrons and has no explanation in classical physical tenns. Tuimelling has been experimentally observed in many physical systems, including both semiconductors [10] and superconductors [11],... 

An explanation for these size-dependent optical properties, tenned quantum confinement , was first outlined by Bms and co-workers in the early 1980s, [156, 158, 159, 160 and 161] and has fonned the basis for nearly all subsequent discussions of these systems. Though recent work has modified and elaborated on this simple model, its basic predictions are surjDrisingly accurate. The energy of the lowest-lying exciton state is given by the following simple fonnula ... 

The electronic spectrum of the radical has been recorded long before a satisfactory theoretical explanation could be provided. It was realized early on that the system should be Jahn-Teller distorted from the perfect pentagon symmetry (D5/, point group). Recently, an extensive experimental study of the high-resolution UV spectrum was reported [76], and analyzed using Jahn-Teller formalism [73],... 

The following sections give an overview of the functional form of the PFF and a short explanation of the various contributions to the total force field energy of a molecule or molecular system. 

The classical architecture of an expert system comprises a knowledge base, an inference engine, and some kind of user interface. Most expert systems also include an explanation subsystem and a knowledge acquisition subsystem. This architecture is given in Figure 9-34 and described in more detail below. 

Besides these three major components, many expert systems also comprise an explanation subsystem and a knowledge acquisition subsystem,... 

Mathematical derivations presented in the following sections are, occasionally, given in the context of one- or two-dimensional Cartesian coordinate systems. These derivations can, however, be readily generalized and the adopted style is to make the explanations as simple as possible. 

All three equations, and others, have been used to characterize chromatographic systems, with no single equation providing the best explanation in every case. ... 

The answer, very often, is that they do not obtain any intensity. Many such vibronic transitions, involving non-totally symmetric vibrations but which are allowed by symmetry, can be devised in many electronic band systems but, in practice, few have sufficient intensity to be observed. For those that do have sufficient intensity the explanation first put forward as to how it is derived was due to Herzberg and Teller. 

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