Types Of Compounds Research Articles

Fen—an axiomatic basis for program semantics

A formal system is presented which abstracts the notions of data item, function, and relation. It is argued that the system is more suitable than set theory (or its derivatives) for the concise and accurate description of program semantics. It is shown how the system can be used to build composite data types out of simpler ones with the operations of rowing, structuring, and uniting. It is also demonstrated that completely new primitive types can be introduced into languages through the mechanism of singleton data types. Both deterministic and nondeterministic functions are shown to be definable in the system. It is described how the local environment can be modeled as a data item and how imperative statements can be considered functions on the environment. The nature of recursive functions is briefly discussed, and a technique is presented by which they can be introduced into the system. The technique is contrasted with the use of the paradoxical combinator, Y . The questions of local and global environments and of various modes of function calling and parameter passing are touched upon. The theory is applied to the proof of several elementary theorems concerning the semantics of the assignment, conditional, and iterative statements. An appendix is included which presents in detail the formal system governing webs and fen , the abstractions used informally in the body of the paper.

The role of chemistry in plant systematics

Although the hybrid discipline of biochemical systematics has been a distinct field of study for only about ten years, it has had a telling impact on taxonomic practice. Nevertheless, the chemical approach, with its emphasis on the exact, tends to exlude much of the wealth of natural phenomena that are the backbone of taxonomy. It is necessary for the chemist and biochemist to acquire a better understanding of the nature of classification before undertaking surveys. More thought on infraspecific variation is also required, and the tentative nature of most phylogenetic proposals needs to be more widely appreciated. These problems are discussed in relation to recent studies involving different types of chemical compounds, including proteins, and suggestions are made for future priorities in chemotaxonomic research.

Quantitative two-dimensional thin-layer chromatography of deoxyribonucleic acid components

In studying the various parameters of normal and malignant mammalian tissues, it became apparent that there was a need for a rapid quantitative procedure for the determination of deoxyribosides and deoxyribotides. A new technique, thin-layer chromatography (1), has shown great versatility in the separation of different types of chemical compounds. Application of this technique for the separation of various ribonucleosides and ribonucleotides has been recently reported by Randerath (2, 3), but his procedure does not give sufficient resolution for quantitative determination. We wish to report a two-dimensional thin-layer chromatographic method for the quantitative determination of deoxyribosides and their 5′-phosphates.