Knowledge manipulation

The mechanistic aspects of nucleophilic substitution reactions were treated in detail in Chapter 5 of Part A. That mechanistic understanding has contributed to the development of nucleophilic substitution reactions as importantl synthetic processes. The SN2 mechanism, because of its predictable stereochemistry and avoidance of carbocation intermediates, is the most desirable substitution process from a synthetic point of view. This section will discuss the role of SN2 reactions in the preparation of several classes of compounds. First, however, the important role that solvent plays in SN2 reactions will be reviewed. The knowledgeable manipulation of solvent and related medium effects has led to significant improvement of many synthetic procedures that proceed by the SN2 mechanism. 

Knowledge manipulation, as important as the definition of the knowledge domain, Is implemented by a rule interpreter consisting of three parts, namely a pattern matcher prompting the rules to be applied in each situation, a filter determining which rule of several possible Is to be applied and an executor eventually applying the rule. 

The methods have in turn launched the new fields of nanoscience and nanoteclmology, in which the manipulation and characterization of nanometre-scale structures play a crucial role. STM and related methods have also been applied with considerable success in established areas, such as tribology [2], catalysis [3], cell biology [4] and protein chemistry [4], extending our knowledge of these fields into the nanometre world they have, in addition, become a mainstay of surface analytical laboratories, in the worlds of both academia and industry. 

The most recent version of EROS has a clearcut separation of the system proper, which performs all the manipulations on chemical structures and reactions, from the knowledge base, which defines the scope of it.s application (Figure 10.3-7). 

Definition / An expert system is a computer program that manipulates large amounts of symboHc knowledge using quaUtative techniques, to solve problems that can otherwise be solved only by expert human problem solvers. Expert systems capture the human problem solver s expertise in the form of domain-specific knowledge and domain-independent problem-solving strategies. 

Definition 2 Knowledge-based systems are computer programs that encode symboHc knowledge about domains and tasks, and solve problems by manipulating this knowledge using quaHtative techniques. 

Definition 2 is phrased in terms of knowledge-based systems rather than expert systems. No reference is made to expert human problem solvers. Definition 2 captures the sense that the representation and manipulation of knowledge is the source of such a system s power, whether or not that knowledge is dkecdy eHcited from a human expert. 

Designs should be based on knowledge of what the human body (and human nature) will do. Include educated operators in design reviews. The HAZOP methodology for process hazard analysis offers an excellent opportunity to identify design and procedural opportunities for inherently safer systems. After all, the OP in HAZOP stands for operability (COPS, 1992). For example, a safe start-up procedure that requires the operator to walk up and down the stairs three times to manipulate valves in the correct sequence can be made inherently safer by locating the valves so that operator has to walk up the stairs only once during the start-up. 

There can be no set standard or measurement for all types of filth and filth elements, nor can any one procedure be employed, any one set of circumstances considered, or any one kind of evaluation applied. In any case, however, it is of prime importance that a thorough study of method precede manipulation furthermore, it is highly desirable that the operator have sufficient knowledge of production and storage conditions to draw logical and supportable conclusions from the filth elements recorded. Obviously, degree of infestation or rot could not be expected to follow with mathematical exactitude the constant curves found in other sciences. 

The role of the chromatographer is therefore, based on a knowledge of the analytes under investigation, to manipulate the properties of the stationary and/or mobile phases to move from these extremes and effect the desired separation. 

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