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This thesis examines Lagrangian-mean flows induced by surface gravity waves, with particular emphasis on the displacements associated with these flows. Stokes drift, the small Lagrangian-mean velocity accompanying the orbital motion of particles beneath surface waves, has been well-studied, and is proven to play a role in ocean transport. However, Eulerian-mean flows induced by slow variation of the wave field (divergence-driven), viscous effects, or geophysical effects such as density stratification and planetary rotation, have received less attention. It is the aim of this thesis to study these wave-induced Eulerian-mean flows, which must be superimposed on the Stokes drift to obtain the correct Lagrangian-mean (or mass transport) velocity induced by surface gravity waves. In Chapter 2, the effects of wave directional spread and density stratification on the mean flow induced by a surface gravity wavepacket in deep water are studied, and the corresponding displacements are derived. Chapter 3 examines 'Ekman-Stokes' dynamics driven by the Stokes drift and Coriolis force within the turbulent upper ocean boundary layer, and uses buoy data to explore the impact these dynamics have on the drift of a floating particle. Finally, in Chapter 4 I combine the insights of the two previous chapters to develop an analytical model capable of describing both divergence-driven and geophysically-driven Eulerian-mean flows induced by surface waves.

Two new fluorescent-labelling techniques for studying peptide transport are described. A peptide transport system has been demonstrated in a higher plant tissue, the scutellum of germinating barley embryos. This system has been extensively characterized, and found to have many similarities to peptide transport systems in microorganisms and mammalian tissues. Evidence has also been obtained for the existence of a peptide transport system in the membrane of an intracellular organelle, possibly the vacuole. Peptide transport is an active process and appears to require the production of a proton gradient across the plasmalemma. Disruption of the proton gradient not only inhibits peptide transport, but also causes general exodus of amino acids from the embryo and affects amino acid metabolism. Considerable pools of small peptides have been detected in both the endosperm and embryo of the germinating barley grain. The concentrations of peptides achieved in the endo sperm are of the right order of magnitude for the efficient operation of the peptide transport system. It seems that the uptake of small peptides by the scutellum of germinating barley embryos is of considerable importance in the transfer of nitrogen from the endosperm to the embryo during the iLobilization of zhe protein storage reserves.

This paper is addressed to the problem of how it is possible to conduct coherent, purposeful conversations. It describes a computer model of a conversation between two robots, each robot being represented by a section of program. The conversation is conducted in a small subset of English, and is a mixed-initiative dialogue which can involve interruptions and the nesting of one segment of dialogue in another. The conversation is meant to arise naturally from a well defined setting, so that it is clear whether or not the robots are saying appropriate things. They are placed in a simple world of a few objects, and co-operate in order to achieve a practical goal in this world. Their conversation arises out of this common aim; they have to agree on a plan, exchange information, discuss the consequences of their actions, and so on. In previous language-using programs, the conversation has been conducted by a robot and a human operator, rather than by two robots. In these systems, it is almost always the human operator who takes the initiative and determines the overall structure of the dialogue, and the processes by which he does so are hidden away in his mind. The aim of our program is to make these processes totally explicit, and it is for this reason that we have used two robots and avoided human participation. Thus the main focus of interest is not the structuring of individual utterances, but the higher-level organisation of the dialogue, and how the dialogue is related to the private thoughts which underlie it. The program has two kinds of procedure, which we call ROUTINES and GAMES, the Games being used to conduct sections of conversation and the Routines to conduct the underlying thoughts. These procedures can call each other in the normal way. Thus the occurrence of a section of dialogue will be caused by the call of a Game by a Routine; and when the section of dialogue ends, the Game will exit, returning control to the Routine which called it. There are several Games, each corresponding to a common conversational pattern, such as a question and its answer, or a plan suggestion and the response to it. The Games determine what can be said, who will say it, how each remark will be analysed, and how it will be responded to. They are thus joint procedures, in which the instructions are divided up between the robots. When a section of dialogue occurs, the relevant Game will be loaded in the minds of both robots, but they will have adopted different roles in the Game, and will consequently perform different instructions and make different utterances.

It is argued that a visual system, especially one which handles imperfect data, needs a way of selecting the best consistent combination from among the many interrelated, locally plausible hypotheses about how parts or aspects of the visual input may be interpreted. A method is presented in which each hypothesis is given a supposition value between 0 and 1. A parallel relaxation I operator, based on the plausibilities of hypotheses and the logical relations between them, is then used to modify the supposition values, and the process is repeated until the best consistent set of hypotheses have supposition values of approximately 1, and the rest have values of approximately 0. The method is incorporated in a program which can interpret configurations of overlapping rectangles as puppets. For this task it is possible to formulate all the potentially relevant hypotheses before using relaxation to select the best consistent set. For more complex tasks, it is necessary to use relaxation on the locally plausible interpretations to guide the search for locally less obvious ones. Ways of doing this are discussed. Finally, an implemented system is presented which allows the user to specify schemas and inference rules, and uses relaxation to control the building of a network of instances of the schemas, when presented with data about some instances and relations between them

Recent work in artificial intelligence has developed a number of techniques which are particularly appropriate for constructing a model of the process of understanding English sentences. These methods are used here in the definition of a framework for linguistic description, called "computational grammar". This framework is employed to explore the - details of the operations involved in transforming an representation English sentence into a general semantic Computational grammar includes both "syntactic" and "semantic" constructs, in order to clarify the interactions between all the various kinds of information, and treats the sentence-analysis process as having a semantic goal which may require syntactic means to achieve it. The sentence-analyser is based on the concept of an "augmented transition network grammar", modified to minimise unwanted top-down processing and unnecessary era bedding. The analyser does not build a purely syntactic ,structure for a sentence, but the semantic rules operate hierarchically in a way which reflects the traditional tree structure. The processing operations are simplified by using temporary storage to postpone premature decisions or to conflate different options. The computational grammar framework has been applied to a few areas of English, including relative clauses, referring expressions, verb phrases and tense. A computer program ( "MCHINE") has been written which implements the constructs of computational grammar and some of the linguistic descriptions of English. A number of sentences have been successfully processed by the program, which can carry on a simple. dialogue as well as building semantic representations for isolated sentences.

This work is concerned with the problem of constructing associative memory models which store and retrieve information in a distributed fashion - that is each store location can be involved in the storage of more than one piece of information. The models are to be logically simple in form and efficient in their use of store. It is hoped that those proposed may find a place in neurophysiological theories of memory. From the starting point of seeking a less complex representation of a holographic model of memory called the Holophone, several memory models have been proposed and their properties investigated by analytical and computer simulation methods. All the systems considered belong to a family of memory models which are described by a pair of matrix equations. It is found that the models which perform well are non-linear devices which have to store and retrieve highly redundant information. One of these, the Associative Net, is closely related to a recent theory of the cerebellum. Some of the contents of Chapters 3, 4 and 5 have already appeared in papers published in collaboration with H.C. Longuet-Higgins and O.P. Buneman. Otherwise this dissertation is believed to be original in content and in arrangement.

This work concerns a problem in modelling people's understanding of music. The problem is cast in the terms of discovering formal rules for transcribing melodies into musical notation, as this might be done by a student in a harmony class, taking musical dictation from a 'deadpan' performance on the keyboard. The score that results reflects important aspects of the structure and interpretation of the piece, which are only implicit in the performance. In Part I it is argued that this paradigm raises questions of general relevance to the study of our perception of music. In carrying out the task of notating a piece, two kinds of problem arise: what are the harmonic relations between the notes, and what are the metric units into which they are grouped? These two problems are considered in isolation from one another. In Part II, algorithms which embody two kinds of rule for the inference of metre are presented . In Part III the harmonic problem is considered. It arises from the fact that the number of keyboard semitones between two notes does not, by itself, identify their harmonic relation, which is what the notation has to express. Among other considerations, the key of the piece is an important characterisation of this identification - but the key is not explicit in the performance, and must itself be inferred. An earlier theory of harmonic relations is further developed into algorithms for assigning key-signatures and notation to melodies. By -the definition of the problem, we are committed to the concern of music belonging to the tradition of Western tonal music, to which the idea of key applies. Most of' the musical examples discussed will be taken from the work of one of its outstanding exponents, J.S. Bach, and in particular we shall be dealing with the fugue subjects of his “Well-Tempered Clavier". Some of the contents of Part II, Section § 2, and of Part III, Section § 3, have already appeared in a paper published in collaboration with H.C. Longuet-Higgins. Part III, Section § 2.1, describes his prior work in formulating the theory of harmonic relations, mentioned above, which forms the foundation of the work described in that section and has been published elsewhere by him.