Evidence is presented that supports the view that most models of short-term memory cannot account for the flexibility of the primary memory system. It is argued that the working memory model outlined by Baddeley and Hitch (1974) is, however, a potentially adequate model. Working memory, in this thesis, is depicted as a system that assembles 'constellations' consisting of the central executive and one or more sub-systems. This view suggests a formulation that is considerably more complex than the 1974 model. The empirical studies examine the role of the visuo-spatial scratch pad in the formation and maintenance of working memory constellations. It is concluded from these studies that the scratch pad is independent of the articulatory loop but is usually coupled to the central executive except during maintenance rehearsal. Furthermore, it can be used concurrently with the articulatory loop to process spatial aspects of highly verbal tasks. However a constellation consisting of the executive, the loop and the scratch pad is vulnerable to a wider range of interference effects than a simpler constellation. Paivio (1971) suggested that 'dual coding' leads to better memory performance, however, this is only the case when no distractors are present. The final two chapters present some speculations on how working memory research might proceed in the future. It is concluded that the current trend towards collecting convergent evidence and the emphasis on testing theory in applied situations should give us insights into memory that were not available to Ebbinghaus and other early memory researchers.

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The world of software is increasing and the requirements on software systems are getting harder. To ensure that these requirements are fulfilled, we use program verification. The goal of verification is to prove that the system automatically fulfills its requirements. In this thesis, we will consider parameterized systems. A parameterized system is a system that contains an arbitrary number of components (processes) organized according to a particular pattern. Such systems are heavily used to implement mutual exclusion protocols [1,2]. In this thesis we will extend parameterized verification to handle variables over unbounded data domain. In fact, there is a large number of protocols (or programs) that manipulate variable over unbounded data domain. An example is the Bakery[2] protocol which uses integer variables to decide the order in which the processes are allowed to enter their critical section. In order to handle the unbounded data domain, we use abstract interpretation. The key idea is to abstract away the variable values and only keep their internal relationships. Finally, we have constructed a prototype in C and tested it again on a number of mutual exclusion protocol.

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